If I had a dollar for every time this question is asked ...
As references, I've listed a wealth of sites with a wealth of project ideas. Thanks to Former MN Science Teacher for many of them. Check out the past winners/entrants at the scisvc.org site for more difficult projects. If you find better references, please tell me.
Be creative. Don't waste this extremely valuable experience by copying someone else's idea. Focus on what interests you. Choose the best and most interesting project that you're confident you can accomplish in the time allowed. And allow plenty of time. A really good science project looks very good to college admissions officers, especially if the fair judges agree and award you a prize. You want to show that you can think, reason, manage a project, do proper experiments, write your results clearly and accurately, and that you're willing to work. Do your own research. Do your own work. Get help and get advice. Teachers and people in industry are often very willing to give advice and to make equipment and facilities available to someone who really cares about their project. It's a great experience.
(YA limits me to 10 links, so I split them between the answer and the references.)
http://www.sciencebuddies.org/
http://www.all-science-fair-projects.com/
http://www.usc.edu/CSSF/Resources/GettingStarted.html
http://school.discoveryeducation.com/sciencefaircentral/
http://www.scienceproject.com/
http://www.energyquest.ca.gov/projects
http://www.freesciencefairproject.com/