TubeTV is a freeware program for Mac OS X which enables you to search for, save, and convert YouTube and other flash videos to a format suitable for playback on your favorite devices.
Disruptive technologies, pedagogical innovation: What's new: Findings from an in-depth study of students use and perception of technology. Computers & Education 2008 50 (2): 511-524.
Screencast-O-Matic is a new web-based screencast program that is incredibly easy to use. And since it uses a Java applet, it runs on Windows, Mac, and Linux machines.