I have no shortage of ideas, but it should be something that you personally have an interest in. You'll do a better job because it'll be fun instead of just an assignment. What are your hobbies? Anything that you like to do has a basis in some branch of science, from kite flying to bowling to billiards to archery. Even building models involves the chemistry of adhesives and paints, and reading comic books brings up all sorts of possibilities for experimenting to see why someone can't do something like fly or spontaneously combust.