To give yourself enough time to adequately prepare and submit all the scholarship applications you will likely fill out, you will need to plan ahead.  If possible, start during your JUNIOR YEAR.  Although the information may change some by your senior year, you'll have the deadline, a copy of the application, and a person to contact to get more information.  This will give you a good idea what to expect next year from that scholarship, and you'll be able to request information early in your senior year.  One strategy I suggest you try is to locate someone in the class above you who will be applying for numerous scholarships (the more like you they are, the better - major, college choices, GPA, ACT/SAT, etc.), and offer to help them find scholarships.  In return, after they're done with everything, they agree to pass it along to you.  I wrote a column about it here.

You can work together or independently, but you will both search in magazines aimed at teens, check with local organizations that might award scholarships, contact professional organizations related to your major, scour the Internet for information, check out scholarship books from the library, obviously check your colleges' web sites, and most importantly, stay in touch with your high school counselor. Also check with your church (if applicable) at the local, regional and national level.

Your counselor will be your best friend in this process.  Much of the information on local scholarships will come through your counselor, but you'll also need recommendation letters, will want to have them read over your essays and responses, and they may want to know what you've done in this area.  If you're smart (and nice), you'll offer to help your counselor with anything to do with scholarships and/or college admission for all of his/her students.  You could offer to type their newsletter, update the counseling web page, make announcements, distribute applications to your classmates, etc. That way you'll be among the first to know about everything new.

Some other helpful hints include:

• Save, print or copy all applications before you send them
• Before you submit an online application, double check to ensure you catch any type-o's or obvious mistakes
• Don't hand-write scholarship applications (admission applications you could get by with this, not so for scholarships)
• On recommendation letters, contact those you want to have write letters for you early to ask, then give them plenty of notice when you need a letter, and give them a copy of your resume ahead of time
• Always have someone else read over your application to make sure you don't miss something obvious
• Start working on scholarship applications far enough ahead of time so you won't be rushed

Below are links to several scholarships I'm aware of.  I'll be adding more as I become aware of them. 

Coca Cola Scholarship - This is a well-established, prestigious scholarship worth between $10,000 and $20,000.  250 are available for those attending 4-year schools.  There are also 350 smaller scholarships available for those attending 2-year schools (check the web page for details on nominations).