Philosophy:
Lao Tzu - Dao de Ching
Aristotle - Nichomachean Ethics
Leonard Peikoff - Objectivism: The Philosophy of Ayn Rand (I was first influenced by Rand's fiction which is good to get a sense of her spirit, especially Anthem which is concise, but for a non-fiction treatment I think Peikoff best)
Richard Dawkins - The Selfish Gene (but ignore his baseless protests to reject the moral implications of his scientific work and his pleas to retain Christian morality)
Language:
Marshall Rosenberg - Nonviolent Communication
Investing:
Ben Graham - The Intelligent Investor
Jim Rogers - Hot Commodities
Money & Banking:
G. Edward Griffin - The Creature from Jekyll Island (among many others, but this was first)