Sanyo do some fully waterproof camcorders and while they're bigger than helmet cameras they have much better resolution, stabilisation, night shot, etc.
VPC-WH1
http://sanyo.com/xacti/english/produ...wh1/index.html
VPC-CA9
http://sanyo.com/xacti/english/produ...ca9/index.html
There's a good resource by PeteF. on his website especially regarding the links to on helmet camera cases.
http://www.petefagerlin.com/helmetcam_video_how_to.htm