This thread is has been alright for awhile... but I love books. So I don't care. ::Grinn::
The Baroque Cycle by Neal Stephenson
It should be required reading for life, IMO.
Stephenson also wrote Diamond Age, another great piece of fiction that really messed with my head.
Smoke and Mirrors by Neil Gaiman
Anything, anything ANYTHING by the author/poet/second-coming, Ray Bradbury. Everytime I re-read his books, it freaks me out... In particular, everytime I read Fahrenheit 451, my life changes drastically.
H.P Lovecraft wrote some amazing short stories, though I never did get around to The Mountains of Madness...
Resume with Monsters and Zodwallop by William Browning Spencer I remember as being pretty entertaining and thoughtful, a combination I haven't seen very often, though I haven't been able to find a copy for years...
Finally, there's a book by Suzanne Clarke called Jonathon Strange and Mr. Norrell, that I bought at random one day, and blew my mind. I think that's the best part of books... It's like russian roulette. Never know if you'll be the same person at the end of them.