+1 for Zen and the Art of Motorcycle Maintenance, Great book with some a deeply personal tale that ALSO serves as a good primer for Western philosophy.
Another good survey book is The Wisdom of the West by Bertrand Russell.
Robert Nozick is fantastic about the spirit of questioning. I recommend starting with his book The Examined Life. His book on political philosophy, Anarchy, State, and Utopia is also infused with the ability to ask interesting questions.
If you have a background in science, programming or music, I would also look into the stuff by Douglas Hofstadler. I think I'd start with I am a Strange Loop, but his magnum opus is Godel, Escher, Bach.
Despite his reputation, I find Foucault easy to understand. Look into Discipline and Punish.
The Book by Alan Watts gives you a good portal into Eastern thinking.
Hard to leave out Nietzsche. I would start with Beyond Good and Evil, but you can also cut your teeth on The Birth of Tragedy.
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The Masters 2015
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