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.
Matt Unsworth offers a set of free wargames rules called The Few that he uses with his students to simulate the Battle of Britain.
Matt Fritz offers a set of fast play miniatures rules for World War II Aerial Combat.