Hello there, 
That's a good idea! I do have one book, one and only: "Modeling Realistic Tanks and Artillery" by Mike Ashey. I bought it from Amazon. Quite good with illustration, but then it would be more useful for beginners. 
Other than that, I do get some mags here and there, mainly if they feature some specific builds i loved, like Tiger 1 etc. 
Let's see the responses from the rest...
Cheers!