Schneier on Security, by Bruce Schneier. A great, though dated, text on the dilemmas inherent in securing the nation.
Nothing to Hide: The False Tradeoff Between Privacy and Security, by Daniel J. Solove. I like this book better than Solove's Understanding Privacy, because it focuses on the security state specifically. It's also interesting in it's rejection of the notion of a tradeoff between privacy (liberty) and security. A quick, interesting read.
Ghost Wars: The Secret History of the CIA, Afghanistan, and Bin Laden, from the Soviet Invasion to September 10, 2001, by Steve Coll. Another dated, but celebrated work - which I have been too long in putting off reading. The detailed insight in this eminently readable narrative is one reason why Coll received a Pulitzer Prize for his writing in Ghost Wars.