1984, The Hitchhikers Guide to The Galaxy and the Diskworld series are my personal favorites.
I don't really get the second one.
The hitchhikers guide to the galaxy? I didn't read the books, only saw the film, and it was funny enough. But my friends tell me that the books are better.
I really liked "The Unbearable Lightness of Being" by Milan Kundera. It's a really interesting book.