Don't think this classifies as a book, but it is a good reference, and I'm not sure where else to put it.
I'm sure a lot of you already know about this, but as I was poking around the web, I ran across this site:
Prime Portal - The Military Enthusiast Modeler's Reference Site
Hundreds of walkaround photo sets, not only WWII aircraft, but all sorts from the early days of flight to the newest YF-whatever, and not just aircraft, but anything military.