I don't know that this is an all-time list; more of a here and now list.

Fiction

The Adventures of Huckleberry Finn, Twain
A Confederacy of Dunces, Toole
Of Mice and Men, Steinbeck
The Hobbit, Tolkien
Master and Margarita, Bulgakov

Non-fiction

The Structure of Scientific Revolutions, Kuhn
Anti-Intellectualism in American Life, Hofstadter
The Problems of Philosophy, Russell
The Worldly Philosophers, Heilbroner
Betraying Spinoza..., Goldstein