My favorite books are:

1. Thus Spoke Zarathustra by Friedrich Nietzsche
2. The Essential Writings of Ralph Waldo Emerson
3. Tao te Ching by Lao Tzu
4. Guns, Germs, and Steel by Jared Diamond
5. Frames of Mind by Howard Gardner

For writing, I’d probably get a copy of The Elements of Style by Strunk and White, and The Elements of Eloquence by Mark Forsyth