Kahn Academy has been making videos for years.
I have used these videos many times as introductions to various lessons, or to help myself understand a concept before teaching it. Here is an example:
While the videos are a great tool, Khan has also made a tremendous website that is entirely customizable. While the customizable site does not perfectly fit into my “low tech” parameters, I wanted to give it a try to show low-tech self that I can do hard things. Low and behold, I think I love it.
Check out my screencast for a quick look around to see how you may be able to bring it into your own class.