I know this is an old thread, but I might as well throw in my two cents about Pratchett:
For me, Night Watch is the best of the lot. Not only very funny, but thematically beautiful. Old age, confronting one's past, honouring the fallen, standing up to wrongdoers, doing the right thing not because you have to, but because you know you should. A genuinely brilliant piece of literature. The ending just before *SPOILERS* Vimes travels back to the present damn near had me in tears. Sad, defiant, quietly triumphant.
After that, Eric has to be up there. As a fan of classics, the parodies of Faust and the Illiad especially were quite wonderful. The Truth is excellent as a mirror of the modern media, as well as a play on the way people think and perceive the world. Wasn't a huge fan of Going Postal, actually thought the TV adaptation was better as it cut out most of the rather sluggish first half of the book. Making Money was much better even thought it stuck to a very similar formula. After the Truth my favourites would have to be in no particular order: The Last Continent, Small Gods, Interesting Times, Soul Music, Thief Of Time and Jingo.
As for discworld books in general, I have yet to come across one I have not finished. Even when they aren't very funny, they are very readable and very accessible. One of the best aspects of Pratchett is that he is very good at explaining characters, places or situations very succinctly and often quite humourously, so even if you pick up a book that is not the first in a series, you will often be up to speed very quickly.
Post edited May 16, 2011 by Al1