Puzzle Palace is excellent. Specifically relating to the recent revelations, this book was where I learned of the NSA's "vacuum cleaner" approach, in which all

Puzzle Palace is excellent. Specifically relating to the recent revelations, this book was where I learned of the NSA's "vacuum cleaner" approach, in which all available messages are collected -- in this case, it was trans-Atlantic radio transmissions being monitored by ECHELON. So, an American citizen in the UK calling an American citizen in the US would have their call collected. The approach (collect everything you can at the trunk line or server farm) is very similar to the e-mail collection strategy that's being documented now.