MIG Alley Ace are rules for modern aircraft combat from 1945 to the missile age.
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.