Flying Circus is a set of free wargames rules based on the old Avalon Hill Mustangs game.
Angels 1-5 is a game of air combat over Britain in 1940
The endlessly interesting Junior General site has a new game called Zeppelins Over London.
Thunderbolt and Lightning is a set of free WWII air combat rules.
JD Burgess’ site has a list of major WWII air war campaigns. For each, he has lists of the planes that participated, with links to photos and information.