I have designed a 3D printable GoPro mount and legs for the dji f450 quadcopter frame. With the ability to look straight down. Very minimalistic design, very lightweight. Uses one servo for tilt which is connected directly, no linkages, zero play, thats smooth tilt :-)
If you want a kit, look at this video: http://www.youtube.com/watch?v=GGoAvjM_nIQ
You can download it from here: http://www.thingiverse.com/thing:34562