I am a fan of online instructional videos and pay $25 a month for full access to Lynda.com (these are software and programming tutorials). The challenge can be finding good material and sometimes you have to pay to assure material has been carefully created.
HowToVideo is a site dedicated to videos that explain “how to” do something. The site really organizes AND screens resources. There is an education category that teachers may find helpful – many useful demonstrations are explained.
I became familiar with this site via a post on the ReadWriteWeb and you might read this post for a more general description and an explanation of you can add WonderHowTo you your Firefox browser. The explanations offered are intended to match the topics you are viewing. This might be an interesting option in some situations. I wonder how easy it is to turn the feature on and off?