A lot of good books in this thread and I have read many of them, but in retrospect these 3 titles have had the greatest effect on me: The End of Faith by Sam Harris: Crystallized a lot of things I have been thinking about over the years. Darwin's Dangerous Idea by Daniel Dennett: Really delved deep into what evolution is and the way it affects how everything in the world works. Wherever You Go, There You Are: Mindfulness meditation for everyday life by Jon Kabat Zinn: What is mindfulness? Why is it important and how can you apply it to your every day life (like the subtitle says). Bearded guru in a cave at top of mountain is optional.