Not in Dayton, but a visit to the Wright-Patterson AFB and
Airforce Museum is a must if you have not been.
Go early one day and sign up for a tour of the hangars on base. Before 9-11 you could drive over, but now you reserve a spot on a shuttle bus.
After you sign up, you can check out the maajority of the exhibits while waiting for your bus. The hangars on base house the largest collection of presidential planes, and also most of the expirimental airplanes.