Fully 3d printable self balancing robot powered by with Arduino, controlled by smartphone via Wifi. Designed and made by Jose Julio.
GitHub B-robot repository with all files and code
https://github.com/jjulio/b-robot
Project homepage in Spanish:
http://cienciaycacharreo.blogspot.com.es/2013/10/b-robot-un-robot-equilibrista-impreso_28.html
Here is another 3d printable self balancing robot:
http://diy3dprinting.blogspot.com/2012/06/balancing-3d-printed-diy-robot.html
Jose Julio also developed very interesting computer vision guided AHRobot (air hockey robot):
http://diy3dprinting.blogspot.com/2014/02/diy-air-hockey-robot-from-3d-printer.html