First is books written by former diplomats / intel opporatives. SO many greats!
Second, the intelligence officer's book shelf. In other words, book lists for people studying the various arts of intelligence. Fascinating stuff.
See the text above the filter - "486 Declassified Book Reviews". I assume anything newer than 1995 is still classified.
The magazine was a new discovery for me as well as the annual reading list.
I have found some excellent British authors with roots in GCHQ, but the American ones I have tried reading so far have been all very black-and-white which makes them super boring.