We went to a science museum this weekend, and we bought a simple toy at the gift shop. It basically is a propeller on a stick. To launch it (note that the propeller stays ON the stick, it does not fly off), hold the stick between the palms of your hands. Quickly slide your right hand forward while keeping it pressed against the left hand.
Aside from being a fun toy to watch flying or to try to catch, it is a good practice for hand-eye coordination. You can buy it on Amazon.