Debt: The First 5,000 Years by David Graeber.

I'm cautious to say it changed my life, but it definitely changed my view on many things. I'm more aware of the ubiquity and power of debt, and I can no longer take those for granted.

It's an extremely interesting read and has a broader intellectual appeal, elucidating the roots of money, morality, and the roles of markets, nations, and friends with regard to those.