Khan Academy is an educational website that allows you to learn about a variety of subjects. I have only used the math portion of this website. This site breaks sections of the subject into "skills" that you can master by answering questions on them correctly. You can also add a coach who can monitor your progress. This website is free, which is nice. One thing I do not like is that you are often quizzed on things you have already mastered instead of new things.
Overall I give this site a 4 out of 5 rating.
You can access this site by clicking on the picture above.