It's been a while since I read it, but Big Fish by Daniel Wallace (yes, the book the Tim Burton movie was based on...they're really different, but both amazing) is probably my favorite book ever.

Chocolat by Joanne Harris and One Flew Over the Cuckoo's Nest by Ken Kesey are also great... Two books I was required to read for my contemporary literature class in high school. I really didn't like that class, so they were kind of 'ruined' for me, though. :\

The Discworld and Hitchhikers Guide to the Galaxy series were great as well, although I think I enjoy the humor in them more than the writing iteslf. :)