found some good ones on here, but they all either printed in 2 separate pieces, or held my guitar too close to the wall and it was unstable. Here's my take on a universal single piece guitar hanger.

MK2 added 2/20/13
Improvements:
guitar axis closer to wall for stability
rounded edges to prevent damage to guitar

Issues:
Slic3r does not like this stl file, I must have made a mistake in the sketch up, working on a fix.