When I give my Moon Hoax talk, I use my belt to demonstrate the flag motion. I blow on the belt to show that air resistance is not an issue, then wave it back and forth. It works pretty well.

I also note that in the Apollo footage of the flag moving, the flag flaps up higher than you'd expect given the small amount of impulse from the astronaut. Since a flag on the Earth would have its motion dampened by both gravity and air resistance, this indicates that the footage was shot in an airless, low-gravity environment. Duh, I'm guessing this means the Moon.