For the really big boys there is a suction cup (they say "SeaSuckers are vacuum cups, not suction cups.") available that is even more solid than the (already rock solid) recommended RAM Mount:
That picture makes the RAM Mount look like a weak solution (which it is definitively not)...
I received some of the SeaSuckers from my friends at Optrix and can say they are really super solid and huge (you need a big windscreen to keep a reasonable field of view
). I'm told you can mount it outside your car driving at 200 mph
The Optrix prepared version is avaiable here http://www.optrix.com/store/super-sucker-xd5
Just in case someone is interested in mounts like this.