I think the Osprey "Aircraft of the Aces" are some of the best - but here are a couple "comprehensive" recommendations:
If I had to get one reference book on WWII aircraft, this would be it. Lots of info, photos, and illustrations – text and pics. I picked it up a couple months ago in the “Bargain Books” section of a Borders store - $9.99. (The link below is to a hardback version on Amazon.)
http://www.amazon.com/Encyclopedia-A...e=UTF8&s=books
These are well worth looking at. I’ve also seen them in the Bargain Books sections of Barnes and Noble stores - $5-6??? Several illustrated paint schemes on the more popular WWII aircraft. I have these 2, but not the one on British aircraft of WWII.
American aircraft -
http://www.amazon.com/Concise-Guide-...e=UTF8&s=books
$2.00 and shipping.
http://product.half.ebay.com/Hamlyn-...18537QQtgZinfo
Axis Aircraft -
$1.86 and shipping!
http://product.half.ebay.com/The-Ham...14483QQtgZinfo
I like this one. Brief easy-to-read 2 pages per aircraft. Comparisons of similar aircraft. Not the deepest on info, but decent all-round reference.
http://www.amazon.com/Aircraft-World...243581-2855849