USA Today includes an interesting article about what college admissions officers want to see in college admission essays. Please read this article and start thinking about experiences that you have had that might make good subjects for essays. You might also want to get started on the Autobiographical Essay (listed on the left sidebar). If you start the paper now, you will get a head-start on AP English and the college admissions essay.
http://www.usatoday.com/news/education/2008-07-12-college-essays_N.htm