Some of them are among the best screen recording software available. Most of them are free.
XVidCap for Linux
http://xvidcap.sourceforge.net
http://en.wikipedia.org/wiki/XVidCap
recordMyDesktop for linux
http://recordmydesktop.sourceforge.net
http://en.wikipedia.org/wiki/RecordMyDesktop
Wink for linux and windows
http://www.debugmode.com/wink/
screentoaster
Free Online Screen Recorder
No installaton; java based
http://www.screentoaster.com
CamStudio: for windows
http://camstudio.org
VidShot Capturer 1.0 for Windows
http://www.geovid.com/VidShot_Capturer/
Screen2Exe 3.0 for Windows
http://www.screen-record.com/screen2exe.htm
http://download.cnet.com/Screen2Exe/3000-13631_4-10673120.html
Microsoft Expression Studio EncoderPro for Windows
http://www.microsoft.com/expression/products/EncoderPro_Overview.aspx