Sorry, there are no perfect projects. Besides, the purpose of such an assignment is for you to think up something yourself, not to have some outsider tell you what to do. Start with what you are curious about and think of how that topic can be investigated. Science fair project rules differ from place to place, some requiring an experiment and others more open to things like displays, so check the rules too.
You'll learn a lot more if you come up with your own idea. Good luck.