+1 on the GoPro HD. A friend has one, and they appear to be very much worth the money.

I am pretty sure that they used them on Mythbusters, the most recent episode (Duct Tape Hour 2) - they had them on their helmets when they were walking across the duct tape bridge. The video looked pretty good to me, and apparently they think it's good enough to use on commercial HD broadcast TV. $300 sounds a bit steep but it's not, given the quality.

I have read reports that it stops at 30 minutes when recording at full 1080p HD at 60 FPS, but I wouldn't do that for evidence anyway; even 24 FPS is plenty for evidence.