Practice math skills from Kindergarten math through Calculus. You can also get lectures for Math, Science (Chem, Bio, Physics), and History. This is also the official site for SAT help on the new SAT.
Watch fun and interesting videos on the content of most of your classes.
Homework help site
Get help understanding the books you are reading in class.
Get help in your Foreign Language class. There is also a super cool free app that goes with this website.