World's free classroom. Everything you ever wanted to learn - from videos. Students can practice at this site and search the tutorials effectively. Teachers can track the students' involvement in the site here also. http://www.khanacademy.org/
Wordpress does not allow for the embedding of some videos from certain sites on the web. With Vodpod, you can embed just about anything, even if Wordpress doesn't technically allow it.
Once students sign up with a promo code they have 6 months of "all-access". Currently there does not seem to be a way to extend this in concurrent years without re-applying for a code and having the students sign up with a different email address.