Mostly philosophy, biography, history or psychology. But, as far as fiction--it must have something behind it. I love metaphors and symbolism. Animal Farm by George Orwell is one of my favorite novels.
First and foremost Beat lit. (Kerouac, Ginsberg, Burroughs, Ferlinghetti) Then there's Poetry and writings by Sylvia Plath and Dorothy Parker Philosophers like Nietszche and Thoreau Some of my favorite books are : The Bell Jar, The Catcher in the Rye, Nine Stories, Tales of Ordinary Madness, Naked Lunch, Queer, Prozac Nation, Atlas Shrugged, The Fountainhead, Beyond Good and Evil, Civil Disobedience, etc. etc. And that just barely scrapes the top