I went to a scholarship workshop at my school the other night and they gave us a bunch of information about under-grad acceptance and applications...
Here are some examples of application essays from the big schools:
Brown University: Tell us anything about yourself that you think we should know. Tell us who you are, how you think, what interests you. Do this in your own handwriting.
Harvard Univeristy: As supplementary data please write a brief essay of 200-500 words. You may choose any topic about which you would like to write: Your family, friends, or another person who has had an impact on you; unusual circumstances in your life; the best or worst features of your secondary school; a recent development in your community; a scientific or other problem which you would like to solve; travel or living experiences in other countries; a question we should have asked on our application. Any subject of direct personal importance to you is a good choice.
Massachusetts Institute of Technology: Life brings many disapointments as well as satisfactions. Tell us about a time in your life when you experienced disappointment, or faced difficult or trying circumstances. How did you react to it? Discribe the world you come from. For example, discribe your family, school, community, city or town, and how the world influences your dreams and aspirations.
They also provided
www.samford.edu,
www.vanderbilt.edu, and
www.bsc.edu for more essay topics.
Anyways, those are probably some of the toughest you'll come across...