I have one (Tony Hawk Helmet Cam) that I'm using for on-board video of RC park flyers. The resolutionis only 320x240 @ 15 frames per second when capturing to SD card (32Mb SD card included) or 640x480 @ 15 frames per second when used as a web cam connected to a PC.

The video is surprisingly watchable and the cam comes with some great capture/editing software. I certainly wouldn't pay full price for this camera, which was $90.00AU but I picked one up at the post Christmas sales for only $53.00AU and I think it's well worth the investment at that price!!

All up it weighs in at only 150 grams including batteries, SD card and rubber helmet mounting strap. Without the strap its only 100 grams. Very small and great for RC planes. I'll post a link to some video when I get around to editing it...