Principal Meetings

Screencsast-o-matic
Free, web-based, 15 minute maximum, allows webcam inset with video
Visit the site

Jing
Free, must be installed on a computer, 5 minute maximum
Get the free download

SnagIt
Educator price: $28.95 (or less in bulk), must be installed on a computer, unlimited length allowed (or at least an hour couldn't find a specified time length)
Free trial
Purchase through REMC Save Bid

Camtasia Studio
Educator price: $169.60 (or less in bulk), must be installed on a computer, unlimited length allowed (or at least an hour couldn't find a specified time length), full editing capabilities, allows webcam inset with video
Free trial
Purchase through REMC Save Bid

Various iPad Apps
Free or paid are available with different functionality.  The 21 Things for iPads site has a section on screencasting.  Click here to visit that page.