Talk to your high school's counselor. He or she will have information on a range of available scholarships, combined with a knowledge of your academic and personal situation. Discuss your college plans with your counselor, stressing the need for a grant or scholarship, and he or she should be able to recommend some places to apply.
Consult the financial aid departments at universities you intend to apply to. Scholarships may be specific to a university (for instance, scholarships offered by alumni associations), and the financial aid office will have the most up-to-date list for the university.
Check the U.S. Department of Education's website. The Department maintains a list of useful links for finding grants and scholarships, including a free search tool.
Consult local nonprofit organizations; some clubs, charities and civic bodies offer full or partial scholarships to local students. Companies may also sometimes offer scholarships for the children of employees.
Conduct your own research using local libraries and Internet searches. Ask your school or local librarian if they have any information on scholarships -- announcements are sometimes posted in libraries. When searching online, be specific in your searches, targeting the schools you want to attend, the region you're from or any specialized interests you may have.