Fraps alternative, that doesn't cost anything:
http://l2citadel.com/forums/topic/1026- ... n-the-fly/
Uses the x264 codec, which saves harddisk space and you can prebuffer videos into your RAM. If you hit the record button, the last xy seconds/minutes before hitting the button will also be recorded.
Edit: uses possibly more CPU power than fraps because of the advanced codec, but shouldn't be a problem nowadays. I tested it with 4 and 8 cores with 1080p and had no performance loss when prebuffering to the RAM or actual recording to the HDD.