Mobius hat clip
Update 24. November 2014
Added a second version with an even higher angle. Which one to use depends on the hat and wether you wear it pulled down to your face or loosely.
I used the basic clip shape, but flipped it around and made one side a bit thicker, so it would sit tighter (might give problems using PLA, I printed in ABS).
I also used this Mobius mount: http://www.thingiverse.com/thing:340676
Just a bit of double sided tape and it will stick nicely to it. File down the nubs in front a little to keep it from holding the camera just a bit too tight.
The idea was to let me film my quadcopters.. and since they're generally above me, the camera has to be angled upwards to actually catch the copter.