Cold War, WWII, WWI, post-Cold War, post-9/11. This could be West, East, Third World.
One quality work on the Special Operations Executive, making use of substantial interviews with former agents, is Behind Enemy Lines by Juliette Pattinson.
I've just purchased Walter Schellenberg's The Labyrinth he was in charge of Nazi counter-espionage... and it's taking bloody ages to arrive (no doubt Her Majesty's Government are checking my details). But if it's any good I'll say.
There are also quite a few good documentaries online about the 'Cambridge Spies' -