Screencasts - tutorials and movies made while navigating your computer screen, and includes a narration component. Links to sites and software for screencasting:

O'Reilly
http://www.oreillynet.com/pub/a/oreilly/digitalmedia/2005/11/16/what-is-screencasting.html

Screencast Central
http://www.screencastcentral.com/

Screencast entry at Wikipedia
http://en.wikipedia.org/wiki/Screencast

Replay Screencast (software)
http://applian.com/replay-screencast/index.php