Here are a few others that I also use:

http://www.youtube.com/
Maybe obvious, but a lot of people don’t realize the amount of educational content available here.

http://edufire.com/
A service that connect students and teachers in a virtual classroom. Not everything here is free, but there are plenty of free classes as well. They have mostly language classes, but many other subjects are available as well, such as test prep, etc.

http://smart.fm/
A flashcard service that allows you to use lists made by others or brand new lists. The main focus here is for language learning, but lists can, and are, made for any subject.

Thanks again for the lsit!