http://taksi.sourceforge.net/

Taksi is a video capture/screen capture tool for recording 3D graphics applications (such as games). It can capture almost any windows application using DirectX, OpenGL, or GDI and create an AVI file using any installed VFW codec or still frames in PNG.

Open source but windows only.

May be easier to use than VLC and unlike FRAPS, can encode in real time.

VLC can do this also - search for my other posts on the subject.

I have not yet personally tested Taksi but it has a positive reputation and is open source.