The Discworld cycle is a creation of Terry Pratchett and is copyrighted by him (I'm using the names and all only to make people buy the books, honest!). It describes the Discworld (as if you couldn't guess), concentrating in most books on Ankh-Morpork, the Lancre kingdom in the Ramtop mountains and the country of Death.There are also one-book excursions to places like Klatch, Sto Helit, Tsort, the Counterweight continent and so on.

As of today, the cycle comprises of:

Colour of Magic The Light Fantastic Equal Rites Mort Sourcery Wyrd Sisters Pyramids Guards! Guards! Eric Moving Pictures Reaper Man Witches Abroad Small Gods Lords and Ladies Men At Arms Soul Music

Interesting Times Maskerade Feet of Clay Hogfather Jingo The Last Continent Carpe Jugulum The Fifth Elephant The Truth The Thief of Time The Last Hero The Amazing Maurice and His Educated Rodents Night Watch The Wee Free Men Monstrous Regiment A Hat Full of Sky Going Postal

About the cycle in general

The books are written in a light and humorous style, which gets a bit more serious along the way of the series. There are lots of references to cultural customs, literature, film and music -- a complete lists can be found in the Annotated Pratchett File. Most books are intended as parodies (and the first five surely are), but as the years went on, Terry has started to sneak in more and more seriousness. The philosophy presented in them is a sort of cynical humanitarism, the belief that, although mankind might not be naturaly good, there's nothing that should stop us from believing it. You can find out a lot of it in the Quotes section -- I've chosen them specificly for their reflective value.
As far as the humor is concerned, it's always first-class and very witty. Frankly, I don't think anyone except Terry gets all the jokes.

Colour of Magic:

Rincewind, a one-spell wizard and freelance interpreter, meets Twoflower, the Discworld's first tourist. The former's cowardice and the latter's simplicity manage to burn down Ankh-Morpork, but that is only the beginning of their troubles. They journey to the Rim of the World, as dragons, gods and Death await them...
The first book, and, as some say, the best one. Most of it is pure comedy, but Pratchett's philosophical overtones show through. Some of the ideas (like the Guilds fighting and the Assassins having only practical tests) were later contradicted in the Night Watch subcycle. I also have an impression that the Patrician here is not Vetinari. Tests your knowledge of 'serious' fantasy as well. Above all, tremendous octarine fun.
Statistics: Published in 1983, 285 pages in paperback.

The Light Fantastic:

Rincewind's spell gets a little angry at him for nearly dying. Now he must avoid the hunting wizards and get to Ankh-Morpork before the Big Wahooni and the whole Discworld are obliterated. A hundred-year old barbarian and the good-natured Twoflower are the only help he's going to get...
Great! This book is simply wonderful. The serious fantasy shines through the comic foreground as brightly as the Octavo on any thaumometer.
Statistics: Published in 1986, 285 pages in paperback.

Equal Rites:

A wizard is near to death. He reaches the village of Bad Ass, where an eighth son's eighth child has just been born. He cedes his power onto the child and dies, leaving an heir behind him. The only trouble is, Eskarina is more of an heiress... Ten years later, the first female wizard arrives at the gates of Unseen University and demands Equal Rites!
Granny Weatherwax appears for the first time in this story. Just like Ysabell, she will later undergo a great transformation. This is the first non-Rincewind book and it's obvious that the Disc universe was still forming in PTerry's mind. There are several major inconsistencies; the plural of 'dwarf' is written as 'dwarves' (like in Tolkien) instead of the later 'dwarfs' (for example in the Night Watch cycle). And IMHO, Cutangle is the first attempt at Ridcully. The opinions on this book differ greatly; I consider it not obligatory, but for some it has been the successful introduction to the world of the Disc.
Statistics: Published in 1987, 283 pages in paperback.

Mort:

Sometimes even Death can be tired. But an important public service can't be withdrawn on a whim of any anthropomorphic personification. That is why he decides to get an apprentice. Mortimer, also called Mort, gets the hang of the scythe and Binky, but women seem to give him more trouble. Especially if they are his master's eternally seventeen years old daughter and the lovely princess Keli. Mort learns the hard way that objectivity is essential in such a people-oriented profession...
Death is the best! And Mort learns quickly from such an example. The characters are well-developed and the drama is as strong as the comedy. I think the Death cycle is Pratchett's most ingenious work.
Statistics: Published in 1987, 272 pages in paperback.

Sourcery:

The eighth son of an eighth son is a wizard. Everybody knows that. But what is an eighth son of an eighth son of an eighth son? And where does a barbarian hairdresser, a semi-alive hat and a library assistant come into the equation? Come to think of it, the assistant's name sounds familiar... Rincewind!?
Yes, the worst wizard of the Discworld is back and ready for action... but not for the heights that he seems to be dropping from all the time. And if he doesn't do anything, his world may end up in the Dungeon Dimensions. Hilarious as ever.
Statistics: Published in 1988, 270 pages in paperback.

Wyrd Sisters:

Esmerelda Weatherwax aka Granny was never very attached to drama. But a heir to the throne - and his father's ghost - are too much for her. With the help of the young and romantic Magrat and Nanny Ogg (not young, not romantic), she has to do something about it.
This book is something. One of my favourite authors re-writing the work of another -- a must read for any fan of Pratchett and Shakespeare both. Terry touches on the metaphysics of stories, a theme recurrent in the Lancre cycle.
Statistics: Published in 1988, 332 pages in paperback.

Pyramids:

In the final stages of his education as an Assassin, Teppic has enough troubles already. The last things he needs are green feet and the crown of Djelibeybi. But he is the King now, and it's all on his head -- pyramids, dimensional transformations, gods, priests and handmaidens. And it's not as if he's even killed anyone yet...
Teppic is very likeable, and the whole plot devised by Pterry at his best. The examination scene may be some of his most ingenious writing.
Statistics: Published in 1989, 380 pages in paperback.

Guards! Guards!:

Up till now, the Night Watch of Ankh-Morpork consisted only of Capt. S. Vimes, Nobby Nobbs and Sgt. Colon. But with the arrival of Carrot, the seven-feet-tall dwarf with a crown-shaped birthmark and a very sharp sword, things are going to change. And as if that wasn't enough, some people want to get a dragon. And Vimes doesn't feel in the mood for barbecue.
The first of the Night Watch subcycle. Witty, funny and philosophical - as always. Also has some warning in it -- don't call up that which you cannot put on hold. I recommend the bit about a one in a million chance!
Statistics: Published in 1989, 317 pages in paperback.

Faust Eric:

Eric is a fourteen-years old demonology hacker. He wanted to call a demon and demand the standard three wishes - the world, immortality and the most beautiful woman in history. But when the gate opened, Rincewind happened to be passing through that part of the Netherworld. And with him on the loose, anything can happen.
Easier and simpler than most, initially published as an illustrated novel. In my guess Pterry just wanted to get Rincewind out of the Dungeon Dimensions and didn't have time for a full-blown book. But the ideas aren't bad and there's my favourite character in it.
Statistics: Published in 1990, 178 pages in Roc US paperback (slightly smaller volume and larger print than the UK one).

Moving Pictures:

The old guardian died without training a successor. The eternal and mortally dangerous idea got out. Now, Holy Wood is in full swing, "Blown Away" (love story with Ankh-Morpork civil war in the background, produced by C.M.O.T. Dibbler) is filming, and it's up to Gaspode the wonder dog, to save the world and be called a good doggie. And there might not be another day...
Yes! After a slightly sloppy Eric, Pratchett is back in Style. And Gaspode is sometimes even cuter than the Luggage. (All right, sometimes. Now close the lid, please.) And A Thousand Elephants!!
Statistics: Published in 1990, 333 pages in paperback.

Reaper Man:

The Auditors of reality don't like personalities. And Death certainly has one. When he gets the sack, the life force builds up. This causes a strange object to appear in Dibbler's closet. While Death and a new friend of his confront the Auditors and their new creation, Windle Poons (wizard, dead) and the Fresh Start for the Undead Club are busy fighting off the trolleys...
Death rules. Even if He doesn't wear a crown. And what can the harvest hope for, if not the care of the reaper man? Defintely one of my desert-island book list
Statistics: Published in 1991, 287 pages in paperback.

Witches Abroad:

Lancre cycle part 2. All things come in twos, including godmothers. And when Esme Weatherwax and Lilith de Tempscire square off, someone's going to lose more than just her wand...
A little slower than most books, but nevertheless very good. Pterry's twisted look at stories really makes you think...
Statistics: Published in 1991, 286 pages in paperback.

Small Gods:

Omnianism is a great religion. But the only true believer left is Brutha -- and even he finds it hard to believe in the Great Om as a tortoise. Meanwhile the Quisition plans to conquer the continent and stamp out those that think that The Turtle Moves.
Move over, Lucas, John, Mark and Matthew -- here comes Pterry. Touching, funny, inspirational -- you know the usual lithany. The quality of the theological insight can be judged by the fact Pratchett gets quoted in sermons by priests of many denominations. One of my short-list of favorites.
Statistics: Published in 1992, 381 pages in paperback.

Lords and Ladies:

Lancre 3. Magrat is about to marry king Verence, but it is Midsummer Night... no time to dream. Elves are about town, and if anyone thinks that's cool, think again. Elves are terrific. They bring terror. Elves are glamorous. They project glamour. And that turns your brain into cream cheese. Unless you've got something worth fighting for.
Lots of hey-nonny-nonny and blood all over the place. The elves can magic you into reading for hours and hours at end (my mother lost half a night's sleep when I made her read this). Also a nice explanation for the view of the overwhelming majority about elves. I think this is the most serious Pratchett book I've ever read. (I wrote that before Hogfather and later ones.)
Statistics: Published in 1992, 382 pages in paperback.

Men at Arms:

The ethnic minorities are bothering the Patrician. So Samuel Vimes has to enlist a troll, a dwarf (real, this time) and a - uh, technically not a woman. With a royally obsessed assassin on the loose with the Gonne (copyright by Leonard da Quirm), Vimes doesn't know if he'll be in time for his own wedding. And Lady Sybil has a barn full of dragons...
Tremendous fun, as usual. But the parts about the king are really worth reading. For every leader.
Statistics: Published in 1993, 381 pages in paperback.

Soul Music:

Remember Mort and Ysabell? Well, this is their daughter. Susan Sto Helit. A happy duchess if not for the fact that when Death decides to take a vacation, the next of kin has to fill in. And when a young bard finds a strange instrument in a magical music shop, the Discworld trembles before a new, dangerous kind of art. It's wild. It's dangerous. It's called Music With Rocks In It.
Susan takes after her grandpa in cool and style. And the antics of the wizards-rock fans... let's just say that I don't recommend reading this book in a subway station. If it hadn't been for some kind soul catching me by the shoulder, you wouldn't be reading these words today.
Statistics: Published in 1994, 378 pages in paperback.

Interesting Times:

The Agatean Empire is in uproar as the warlords of the Hongs, Sungs, Tangs, Fangs and McSweeneys fight for the throne of the dying emperor. But the one thing they didn't foresee is that in this game of gods the Lady takes a hand. And for her champions, she chooses Cohen the Barbarian and his Silver Horde (500 years of fighting experience in five persons... oh, and a teacher). Meanwhile, the rebellion sends for the Great Wizzard described in the revolutionary treatise "What I did on my holidays". It's just their luck that the author had Rincewind in mind...
OHohohoho! This is just like the old days of octarine and Octavo! Meet the old friends, dust the sword and on goes the show!
Statistics: Published in 1994, 352 pages in paperback.

Maskerade:

As Magrat is temporarily undisposed in the course of her being a queen and having to take care of the royal succession, Granny Weatherwax and Nanny Ogg are looking for a third witch. Their choice is Agnes Nitt, but the girl decides to run away to the city and sing in the opera as Perdita Dream. She must also deal with a phantom who's teaching her all the aries, and a murderer. And the witches are going to Ankh-Morpork for her.
Very nice. Again much philosophy and a good character study. I recommend some reading on opera and musicals as well, or turn to the APF. And the first edition Corgi paperback has a... uh... nice author photo.
Statistics: Published in 1995, 381 pages in paperback.

Feet of Clay:

This time, Commander Vimes has to deal with a poisoning of the Patrician, a homicidal golem and Nobby Nobbs being a real nob. Where is the arsenic? Why do golems write 'Clay of my clay'? Will the Patrician die? Where will the vampire work again?
The poisoning part is a good criminal plot. So are the political affairs. But the golem thread - it's wonderful. It makes you believe in humanity again. And it reminds me a little of Blade Runner - but only a little.
Statistics: Published in 1996, 415 pages in paperback.

Hogfather:

The Auditors of reality don't like humanity. For them, it equals inefficiency.That's why they're employing a twisted Assassin to kill one of the basic belief figures. So Death has to replace him, while Susan and Billious, the god of hangovers, try to find the god of the winter solstice. The one who's blood brings back the spring. If people don't believe in him, the sun will not come up. Even HEX believes. And you'd better watch out, let me tell you why: the Hogfather might not be coming to town.
This is the ultimate Discworld experience. Philosophy, illogical logic, magic, gods, and Death with a cushion up his robe. Wonderful! The best, most fantastic, brilliant, stupendous- +++ Out of complimentary adjectives error +++ Reboot Winter Raven +++ Redo From Start +++
Statistics: Published in 1996, 445 pages in paperback.

Jingo:

Vetinari's terrier, they call him. Still, Commander Vimes of the Ankh-Morkpork City Watch knows about crimes. War qualifies as one, and so does intolerance, mob rule, as well as sacrificing hundreds to reach a personal goal. So they think they can order him about? Well, we shall have to see...
This book is in a style a bit reminescent of Hogfather -- it's funny, it's supposed to be funny, but deep down you feel a bit weird. The only thing I can compare the character development to is the fourth season of "Babylon 5", where suddenly everything's over and it turns out the heroes haven't emerged as unscathed as we supposed. Still, a hell of a reader, and the Vetinari scenes are not to be missed!
Statistics: Published in 1997, 414 pages in paperback.

The Last Continent:

Who is this hero striding across the red desert? Champion sheep shearer, horse rider, road warrior, beer drinker, bush ranger and someone who'll even eat a Meat Pie Floater when he's sober? A man in a hat, whose Luggage follows him on little legs, who's about to change history by preventing a swagman stealing a jumbuck by a billabong?
If your answer is Rincewind, you're right... This is a book primarily for hardcore Rincewind fans. It's very different from the likes of Hogfather and Feet of Clay, more in tune with Sourcery. Does anybody know where I can get a copy of the ballad of Rince?
Statistics: Published in 1998, 412 pages in paperback.

Carpe Jugulum:

Civilized vampyres arrive in Lancre for the christening of Magrat's daughter, little blue men are coming down from the mountains and all Esme wanted was a little peace and quiet.
After the return to the old days in TLC, Pratchett's style is even darker. This book has few funny moments, but is still a wonderful read, especially for the character development -- a must for all who thought the witches had nowhere to go from there.
Statistics: Published in 1998, 425 pages in paperback.

The Fifth Elephant:

There's political trouble brewing in Uberwald, and etiquette suggests that the Ankh-Morporkian representative should be of high rank -- a duke at least. And the only ducal Vetinari can spare is one Samuel Vimes... But the Commander doesn't have time to get bored, as immediately the trouble turns out to be murders, thievery, sabotage and intolerance -- something he's only too happy to fight against. Meanwhile the same affairs call Angua home, and as Carrot follows her, that leaves Colon in charge of the Watch.
A nice and thought-provoking Watch adventure with a lot of insight into the dwarf society as well as a double helping of the usual headology. Need I say it's a good read?
Statistics: Published in 1999, 450 pages in paperback

The Truth:

Can the dwarfs turn lead into gold? In a rather circumspect way, yes. William de Worde learns just how circumspect that way is, as he struggles with the narrative legacy of every journalistic hero from Clark Kent to JJ Jameson.
After a series of "cycle" novels, this one has an all-new cast. It's Ankh-Morpork, so cameos from the City Watch are unavoidable, but our narrator is for the most part William himself. Refreshing, thoughtful and chock-full of brilliant character types.

Statistics: Published in 2000, 444 pages in paperback

The Thief of Time:

There are many chronological inconsistencies on the Disc. Creatures and contraptions from a hundred different time periods exist side by side. This is how it's always been... or is it?
That's for you to read about, and for Susan Sto Helit and Lu Tze to find out.
I have mixed feelings about this book - it just didn't capture my attention somehow. The ingredients were there, but no sparks. On the other hand, many of my friends say it's their all-time Discworld favorite. I guess you'll just have to find out for yourselves!
Statistics: Published in 2001, ??? pages in paperback

The Amazing Maurice and His Educated Rodents:

A plague of rats descends on a town. The town council pays a piper to lead them out and drown them in the river. If the plague was serious enough, they don't make any problems with the piper's reward. And no-one notices the cat that hangs around and makes sarcastic comments when he thinks no-one's listening... right?
Up to a point - which is where the action starts. This is one of my absolute favorites: the way the characters and the plot is handled is truly epic, and don't let the "Children's Novel" tag fool you. This is about the same kind of children's novel as the unabridged Brothers Grimm. If I were to compare it, I think the nearest would be Frank Herbert's Dune.
Statistics: Published in 2001, ??? pages in paperback

The Last Hero:

The Emperor of Agatea has a new quest. Cohen and the Silver Horde ride again, in an attempt to really immortalize their names. That causes some concern to Ankh-Morpork, so a rival expedition is planned - enrolling Leonard of Quirm, Rincewind and Carrot...
The Last Hero is an illustrated novel, and Paul Kidby's images are at least half the fun. It's also a self-proclaimed "Discworld Fable" - Discworld Legend would have perhaps been a better term. The sheer feel of history in the making permeats the story, and narrativium is almost visible on the pages. All in all, tremendous fun - highly recommended. Note: the paperback edition has some extra illustrations.
Statistics: Published in 2002, ??? pages in paperback

Night Watch:

On a very special day a freak accident forces Vimes to relive certain events from his past - though from a radically different perspective. It's a chance to change Ankh-Morpork as we know it... and a desperate fight to keep things just the same as always.
Night Watch is a book that's exemplary of the "new Discworld" trend. It's dark and gritty. The magic is there - in fact it's rather central to the plot - but the focus is on human nature and its darkest sides. Add to this a cynical idealist's view on politics and revolution, and that would be enough for anyone's book. Except Pratchett's - because he offers us tantalizing glimpses of people's pasts (a certain teenage student assassin who's just starting on the road to become the Havelock Vetinari I adore among them), time-travel mechanics and new developments galore. It's certainly a classic and one of my favorites, though if you prefer Rincewind's kind of easy laughter, you might be disappointed.
Statistics: Published in 2002, ??? pages in paperback

The Wee Free Men:

Take a young girl who wants to be a witch. Add a clan of little blue men. Get trouble.
The second "children's Discworld" book reads very much like a junior part of the Lancre cycle. For me Tiffany was a bit grating, but many have enjoyed it.
Statistics: Published in 2003, ??? pages in paperback

Monstrous Regiment:

Borogravia is an old country with an old religion and an old war. In celebrated folk tradition, Polly/Oliver goes off to join the army and find a certain young man. But things are not how they seem, on the battlefield most of all.
This is Pterry's take on wartime movies and books. I was reminded (in a few cases with literal allusions) of Vietnam the most: films like "Full Metal Jacket", "Platoon" or "Apocalypse Now". To this, he added gender-identifications issues presented in an insightful and in-depth manner. All of it is very fun indeed. The ending is somewhat predictable, but the book itself is strong enough to make up for it.
Statistics: Published in 2003, ??? pages in paperback

A Hat Full of Sky:

The sequel to The Wee Free Men, this book is supposed to feature Tiffany's further adventures. Unfortunately, I haven't gotten my hands on it yet.
Statistics: Published in 2004, ??? pages in paperback

Going Postal:

Ankh-Morpork and the clacks network. Beyond that, not much is known
Statistics: To be published in 2004, ??? pages in paperback