I always like to point out great design when I see it, and Mike Smyth's Minimechadon is a prime example. Mike created the little guy to experiment with learning algorithms for walking. The robot weighs 12oz and has 4 degrees-of-freedom.
The mechanical structure is built from brass tubing (which all the wiring runs through, UHMW (a high density plastic material), and PCBs. Perhaps the most striking aspect of the robot is the use of PCBs to create a 3D structure and mount all of the circuits/electronics.
There are other pictures of the MiniMechadon on Mike's website , along with other projects. Be kind to his server though.