* The New Jim Crow by Michelle Alexander - changed how I think about American racism from an abstract concept to reality. Should be required reading.
* The Alchemist by Paulo Coelho - the book I've read more than any other, a beautiful parable about finding one's place in the world.
* Ishmael by Daniel Quinn - although it has many flaws, this book was very effective in making me question some basic assumptions about human behavior.
* House of Leaves by Mark Z. Danielewski - I can't exactly pin down what changed in me, but this book shook me in a way that no other book ever has. In the right situations reading this book can be like meditation.