The Power Game by Hendrick Smith is one that I recently pulled off my shelf and started looking at again. This is a really in-depth look at the way things get done in Washington, especially during the Reagan era. Anyone who thinks they know how government works, or at least how it should work, should read this and see how it really works.
Caveats: the book was written in 1988, so it has dated a bit. The information on PAC's is pretty much history. K-Street lobbyists don't feature as prominently as they should, and of course the days of the 24-hour news reporting and the internet were still in their infancy. Rereading it today, it's amusing to see people like Dan Rostenkowski as major players again, and Newt Gingrich is still a young up-and-coming firebrand. But much of the writing on the Presidential entourage, media damage control, congressional staffers, and the Pentagon is still very much in play. It's really a must read.