Here's an excellent site for all interested in U2 and A-12/SR71 related information.
It's very detailed and goes from testing to training and operations.
Lots of interesting stuff for aviation fans and also a lot of pictures.

For instance, did you know that after the Gary Powers shootdown over Russia, The CIA started trainning Korean pilots to do the U2 overflights of China ? (so that no other american pilots would be lost )