Rationality: From AI to Zombies by Eliezer Yudkowsky - Despite its many flaws, it seems to be the single most intellectually empowering book I've ever read.
The Book: On the Taboo Against Knowing Who You Are by Alan Watts - Gave me spirituality without supernatural beliefs that I can lean on when all else fails. (Someone else mentioned The Wisdom of Insecurity by the same author, it works just as well)
Atlas Shrugged by Ayn Rand - I don't necessarily endorse it either as a work of literature or philosophy, but it gave me a little push that ultimately sent me on a very deep journey exploring my ethical beliefs.
The Book: On the Taboo Against Knowing Who You Are by Alan Watts - Gave me spirituality without supernatural beliefs that I can lean on when all else fails. (Someone else mentioned The Wisdom of Insecurity by the same author, it works just as well)
Atlas Shrugged by Ayn Rand - I don't necessarily endorse it either as a work of literature or philosophy, but it gave me a little push that ultimately sent me on a very deep journey exploring my ethical beliefs.