The most endlessly applicable is probably Sun Tzu's "Art of War". I don't read a lot of political literature, but Michael Crichton's "State of Fear" was a great one about the dangers of politicized science and the climate change debates.
Animal Farm also helped.
The Bible is up there as well, especially the concept of the "Golden Rule".
This post was edited on 11/12 at 2:06 am