What is your favourite book(s)?

Ok, I'm beginning to start a book collection and I'm not talking about Nancy Drew or Twilight books (though I do have them). I'm talking great pieces of literature (like The Great Gatsby, The Lovely Bones, Life of Pi, ect.) So please, tell me your favourite book or any books that you've read that I might enjoy (I'm not picky, just nothing like Gossip Girl, no offence to those who enjoy them).