Gödel, Escher, Bach
The book that made self-reference feel like the most natural thing in the world.
Bookshelf
The Feynman Lectures on Physics
Still the clearest explanation I've read of why anything works at all.
A Mathematician's Apology
Short, a little defensive, and completely right about what makes a proof beautiful.
Surely You're Joking, Mr. Feynman!
Proof that curiosity is a personality trait, not just a research method.
Gulliver's Travels
Satire that still lands, three centuries later.