Commoncraft is a great resource for teachers. The produce, short, simple, easy to understand videos that explain a variety of subjects "in Plain English".
The videos explain things such as RSS Feeds, computer hardware, twitter, and much more. You can view all of the videos on the site for free. If you like them and want to use them in your classroom or for professional development, you can purchase the videos.
The company also creates custom videos and has done work for Google. You can find some of them on Google Video. The topics include Google Reader, Google Docs.