I like Nietszche, Emerson (especially 'Self-Reliance'), Walt Whitman and the Tao Te Ching. For fiction Zorba the Greek and Dune are two of my favorites.
I like Emerson's Circles essay. It's helped me maintain some humility many times.
Kant's CI for ethics.
Tao Te Ching for perspective and focus.
Nonviolent communication by Marshall Rosenberg for confrontation and interpersonal communication. The concept of NVC and, through its negation, violent communication underscores so much of what's currently going on in the world.
