I was just about to recommend The Book of the New Sun but someone beat me to it. I am damn near to stating that it is the best thing I've ever read, and for someone who reads like 40 books a year, that's saying a lot. It's astonishing. Marvellous. Fantastic. Everything just gels. Gene Wolfe is my new idol.
And dammit, a book thread that doesn't mention Clive Barker????? HOW? Imagica is also just about the best damn book I've ever read. The Great and Secret Show too.
And China Mieville is damn fine. His second Bas-Lag book, The Scar, is amazing. Read Perdido Street Station first though.
Jack Vance. Tales of the Dying Earth. Volume 3. Cugel's Saga. But read them all.
Neal Stephenson: Snowcrash, Cryptonomicon, that new Baroque series, The Diamond Age... great stuff.
Graham Hancock - Fingerprints of the Gods. Non-fiction about how aliens possibly helped humanity create civilization. Lots of end of the world stuff too. Pretty damn fascinating.
Grant Morrison - The Invisibles. Yes, it's a comic book. Yes, it's amazing. Get all 7 volumes, despite them costing like $140 total, as you'll read it 100 times, guaranteed.
Neil Gaiman mentioned but no mention of The Sandman? You guys on crack or what? If you want Neil Gaiman, you want The Sandman. It's his magnum opus. It's a work of art.