The Brand Gap / Zag
Mao
Art of War
The Tipping Point
Freakonomics
Call to Action
My Life in Advertising / Scientific Adveristing
Three Billion New Capitalist
I Am American (And so can you)
Perilous Power: The Middle East & U.S. Foreign Policy (by Noam Chomsky and Gilbert Achcar)
Merchant of Death: Money, Guns, Planes, and the Man Who Makes War Possible
Try out Blink or The Tipping Point by Malcolm Gladwell. Good books that really relate a lot to web marketing if you look for the connections. I also give another +1 to Freakonomics, if you haven't read it, it's worthwhile.