Additional webservices are listed on the classroom20 wiki (see wiki tab on top of the page). Check out Presentation. The idea, if I understand correctly, is to have a single place with all relevant information. That's an open wiki, anybody can update that page with the tips given here ;-).
Screencast-o-matic is good. Smartboard users have a utility called Smart Record that makes hi-def WMA or WMV files on PC and Quicktime on the Mac version. Depends if you want to use your cast in a powerpoint/other presentation in which case the Smart software is more versatile.
I know you are looking for a free one but if you get hooked on screencasting and start making alot of them, I highly recommend Camtasia. I use it to make my masterycasts for my students and it is a really user friendly tool. I can produce multiple file formats at the same time ( flash and iPod is what I make), and I find it as a very user friendly tool.
I will check out some of the other options mentioned. Thanks for the info everyone!
Jing is the only one I've used. But it is free, easy, and fun. It keeps the files on a file server, so you can record lessons for a substitute and just give them the URL. It may not always be free, tho. There's some talk of charging for the server, but I'm happy using it now. If they want to charge me, I'll just find something newer and cooler to play with
The problem with Jing as I see it is that the SWF files are proprietory so even if I download them and try to reencode I get only the audio which is a shame! I use SnapzPro on the Mac and an application called OmniDazzle to highlight stuff on screen and darken the background for emphasis