Start here and, once you've read this, let us know what you think would work. Make sure you choose something YOU are interested in. You'll write a better paper!
Ask yourself who is sponsoring the scholarships? Do they have in particular interests they are trying to develope in college students?
If that does not apply, STAY away from controversy: Religion, politics, abortion, et al.
250 words is not a lot, so you can't develope any major issue.
Leaders and ethics.
Natural Resources and why we need to conserve.
Social responsibility in Business
Volunteering in America: Scouts, School, and Food banks. (you can adjust this to meet your interests).
Sorry, nika -- "wold crisis" (world crisis?) is WAY too broad a topic. Topics for this type of application need to be narrow and focused on what interests the applicant.
What are you passionate about? (And forget cheerleading and sports.)
One of my friends wrote a scholarship essay about the stolen babies in Guatemala being adopted by Americans. Another wrote about how she wanted to translate for new immigrants.
Since you're choosing the topic, be sure to choose one that is very important to you and about which you are knowledgable.
I want to add one danger you face in choosing a topic. Make certain you can say what you need in 250 words. The worse thing you can do is get into a big tarpit of a subject, run out of space, then have to end it abruptly. Avoid things like Nika suggested (world crisis, world peace) that books have been written on, and did not conclude the subject.
Certainly I agreed with Bob's suggestions. Some of the best ones I have read have been personal to the writer and on a topic in a narrow subject area about which they are knowledgable.
I am not sure what the scholarship is for, but if you are going to be interviewed don't dig yourself into a hole where you leave yourself open a question that you can't answer. However, if you can leave something obvious unsaid then this is a good opening question for the interviewer.
Some of the better essays I have seen have avoided being too closely allied to the sponsors topic areas as being too close these can come over somewhat false, i.e. 'sucking up' for want of a better phrase.
I like the essay to say something about the applicant as a person, what they are like at the time of writing, so written in the present tense.