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)