PMDL is right. Tis is a tough question. A lot depends upon what type of training you are interested in.
Being a strength type guy I will answer with the following.
For Non-Science books that are just great from a training and entertainment standpoint -
Dinosaur Training - Brooks Kubik
Rock, Iron, Steel - Steve Justa
Power by Paul - A few different training manuals by Paul Anderson
Kaz Quest #1 and #2 - Bill Kazmaier
For people who like a more science like approach -
Super Training - Mel Siff (I have every edition. 
)
Science and Practice of Strength Training - Vladimir M. Zatsiorsky, William J. Kraemer
Quantum Strength & Power Training - Patrick O'Shea
I am sure the list could be a lot longer. The above are the books I have gone back to over and over again and have been incredibly useful.