If you have a Netflix account, (or know someone who has.) You can watch a selection of videos right online. How might this tie in with education you ask? Well, there are hundreds of documentaries to choose from. Offerings from PBS Video, Nature, Discovery Channel, History Channel and many more.
There's a very wide range of titles, some of which I had at one time gone and signed out from the library. Viewing them online doesn't effect the number of DVD's you have from Netflix and you can watch as many as you want!
Note: The Netflix viewer wants to run on Internet Explorer. But If you'd still like to watch it through Firefox there is a cool add-on that turns a tab into IE and works fine.