In yesterday's review of Terry Pratchett's latest Discworld book, Making Money, I mentioned how daunting it must be to be confronted with Pratchett's 33 Discworld novels and try to figure out where to start. Part of the charm of these books is that they're not written in any main sequence, but rather in several interrelated series that follow the lives of many different characters and subplots. Each book does a pretty good job of standing alone, and they all incorporate major characters from other lines as minor characters in their own, which makes the whole thing very meaty and extra fun to read.
In the comments for the post, Techbuzz pointed out the Discworld Reading Order Guide, maintained in several languages by Krzysztof Kietzman of Lspace.org (Pratchett readers will recognize the reference to "Library Space" -- the virtual Borgesian world in which all potential libraries exist simultaneously). This is a remarkably handy little chart -- all the main lines of the Discworld books are laid out in their chronological sequence, with dotted lines showing how each line intersects with the rest. This is an indispensable guide for the Pratchett novice. Link