May not totally answer your request, but I've been loving my Mobius Action Cam.
The reason I mention it, is it's quite small and can be mounted a myriad of ways with available mounts and/or a little ingenuity. Is Helmet mounting an option for you?
I use a Cateye Stealth GPS mounted on a bar fly mount, and then mount the camera upside down below the handlebars on my right hand side of bars with a Minoura Japan ? VC-100 which is surprisingly stable.

Two minor complaints on the Mobius - battery life = :80 minutes; and no screen. But if you can live with these two it takes very good quality HD footage and there is a community of passionate RCers and hobbyists actively developing behind it. The whole thing feels very open source to me, unlike things I've seen in the photo camera world where a Mfr might only deliver a couple very minor firmware updates over the lifespan of a camera/device.