take the free course then CLEP Free Online Courses, College Classes and Video Lessons - Education Portal Academy
The Khan Academy started out as a bunch of YouTube videos. The Bill and Melinda Gates Foundation jumped in with a bunch of funding. Very cool.
I like it. Before I went to the site, I was about to say that the academy needs drills, quizzes, etc to reinforce the videos. If you just watch the videos but don't take a little quiz afterward, you are not learning as much.