Best book you've ever read is a bit of a tall order. It's hard to rank books.
Books that I've really enjoyed:
Anna Karenin - Tolstoy
Crime and Punishment - Dostoevsky (did a couple russian lit courses and loved them)
Metamorphosis - Kafka
Midnight's Children - Rushdie
The Eternal Lightness of Being - Kundera
God of Small Things - Roy
As I Lay Dying - Faulkner
What can I say, I love tragedies.
Non-Fiction
Shakey (Neil Young biography but just an excellent all around expose of the 70s rock'n'roll era)
Please Kill Me (similar to shakey except focuses on the 70s punk scene)