I just received several of the Osprey Publishing New Vanguard Series books today. These are some awesome books with a lot of great info. They also have lots of great illustrations of ships and subs with color paintings that help out a great deal when it comes to accurately painting models (or in my case A&A WaS minis). There's even a cut away drawing in each book that's very detailed and does a great job of clearly illustrating the internals of the subject ship/sub.
Most run between $12 and $18 so they're not terribly expensive.