In Clouds of Glory is a set of free wargames rules for World War One aerial combat.
Fokker is a one-page set of rules for playing miniature games with World War I aircraft.
Mustangs is a classic Air Combat game from Avalon Hill which, like most of their great systems is long out-of-print. Warflag, however, has a set of rules for playing the game in miniature.
Matt Fritz offers a free set of miniatures rules for playing games involving B17 bomber runs over Germany in World War II. Looks like fun.
Phantoms is advertised as a quick and easy air combat game covering the period 1960 to the present.