If you are interested in teaching or learning math or science and you don't know about Khan Academy, you should. It is very simple but fabulously helpful. Salman Khan "received his MBA from Harvard Business School. He also holds a Masters in electrical engineering and computer science, a BS in electrical engineering and computer science, and a BS in mathematics from the Massachusetts Institute of Technology" 1 and he has set out to tutor the world. He has put together over 1200 ten minute YouTube videos where he delves into math and science topics.
This collection of videos and exercises is the ultimate supplement or recap to math/science learning. Even for me, I find if I have forgotten how to take a derivative or how did the Krebs cycle work again?, I can get a quick refresher by watching a video.
check out his website at khanacademy.org
Here is an example of a video on dividing decimals: