Keep going Alex - i'm English and have no idea of what your level of maths is in the US - so one of these links may be a bit too advanced.

I would recommend:

-http://www.nrich.maths.org

This is a maths website with a similar board to this one.

It has monthly problems of varying difficulty and caters for all abilities. The board also has admins from the University of Cambridge who are qutie wise in all things math.

-http://mathworld.wolfram.com/

This is a website containing hundreds of article varying very greatly in difficulty.

Some can be very useful and are quite simple - such as an introduction to complex numbers and calculus. But these can get very difficult very quickly.

If you are hoping to apply for a very good college, reading some of these may aid you in your interview .

There you go, and i better introduce myself.

I'm Chris, just turned 16 from North England with an interest in maths