The Autobiography of Benjamin Franklin – this is the best $8 that you could possibly spend. Franklin’s business advice is timeless.
Atlas Shrugged – regardless of whether you agree with Rand and Objectivism, 1200 pages about the railroad industry gives you a great business perspective.
The Tipping Point – epidemiology applied to everything.
The Long Tail – the economics of the Internet.
Steel Titan – biography of Charles Schwab – history repeats itself.
Predictably Irrational - markets are not the only thing that is irrational. Great book on human hubris.
Permission Marketing by Seth Godin – incredible book on the theory of permission-based communication.