If you are looking for additional instruction in a limited number of courses, I recommend that you take a look at HippoCampus.org. While it does not offer many courses, the ones it does are available for free. With significant course preparation using audio and video components, it is well worth taking a looking.
The subjects areas (with a few courses each) presently offered are:
1. Algebra
2. American Government
3. Biology
4. Calculus
5. Environmental Science
6. Physics
7. Religion
8. U.S. History
Some courses even support Advanced Placement (AP) classes.