Check with the financial aid department of any school you might apply to, or even ones you don't. Many schools list scholarships available to any student attending any school.
Wherever you look for scholarship money online, remember that you should never pay anything. Don't fall for scholarship application fees, matching services, etc. Not all places that charge are rip-offs, but many are, and there's no need to take risks with so many free resources at your fingertips.
Check locally and offline. Online searches are a great tool, but your odds of winning nationally competitive scholarships might be lower than less-advertised local ones. Check with local businesses and community-oriented organizations in your area: Rotary clubs, YMCA, Kiwanis and churches. High school and library bulletin boards and well-connected guidance counselors might also be able to help.
Reuse your work. Apply for a few scholarships, and you'll start to see a pattern. Many want the same information, and essay scholarships may touch on the same themes.
Be persistent. Do the legwork and keep checking every semester. Some scholarships aren't available to freshmen or undecided majors, and new opportunities pop up all the time.
Fill out the Free Application for Federal Student Aid at the start of every year so your school knows you're still interested in grants and other financial aid. Do it early in the spring semester. Need-based aid such as federal Pell grants is often first-come, first-served.