you don't mention what phone you use. contour has an app that interfaces with the iPhone. uses the iphone as the LCD screen for it. remote control of contour via iPhone. very clever. saw it at the REI recently and was impressed. will wait a while before jumping into the big expensive camera's.
http://contour.com/software/mobile/overview
just peeked in their APPS link and now it runs on Android phones too. very clever.
do small video camera's allow you to rotate the lens? if the camera is not level on the helmet your video will be tilted unless you can adjust the image level to the horizon?