I use 2 contourhd and iphone mounted on the tomtom gps mount, so it doubles as GPS if you needed
I use a cruisecam headrest bar that holds the countourhd. It holds one, but you can DIY and remove their mount and put 2 hardware bolts screw into the base of the countourhd's mounts.
http://www.cruisecam.com/products.html
here's another company
http://www.tachyoninc.com/ - they have a 3D camera now.
I only use countour because it profile fits on the barrel of my paintball gun and I use the 2nd one on the mask. Go Pro are good also but it just sticks out more when playing paintball