Pentax Optio WP/WPi/W10 waterproof cameras or Olympus SW 720 are small
and light enough to be mounted almost everywhere including a helmet.
Optio W10 is my main paddling camera.

I've just converted my Pentax Optio W10 into a helmet cam using some
foam and bungee cord. It is an ugly prototype but it works.

Before trying the new helmet cam on water, I performed "extensive land
testing." I shot several video clips during inline skating on a bike
trail along the Poudre River and posted as a 1 minute movie:
http://users.frii.com/uliasz/weblog/...758/index.html

Of course, you can do it with any small digital camera.

Marek
http://fit2paddle.com