Go Pro
Please have a good look at the stock go pro housings before you buy and take almost all advise so far with a pinch of salt. Non of the standard. Doors or cases allow access to any of the connectors on the camera. Some of the e bay generic ones have holes in the side to allow this. You can do a lot with a dremel though as has been said. I don't know anything about the non standard mounts that have been mentioned aimed at pilots or whoever but again make sure that if you want to access is possible to the connectors. I make specialist leads for the GoPro as part of my business so have looked at this a lot. Most people could knock something up just check before you spend money.
Ps
One slight lie. The new housings that just rap around the sides of the camera do allow access to the 30 pin connector in the back. If you can solder I can give you the pin out diagram.