If you haven't checked out Khan Academy yet, it is definitely worth a look.
Khan Academy includes a library of videos that covers K-12 math, science topics such as biology, chemistry, and physics, and even finance and history. Each video is about 10 minutes long and meant to be viewed on a computer.
This is an extremely informative blog post written by Dolores Gende about Khan Academy and how it could be used with small or large groups in an educational setting.
