Dexter is a dynamically balancing robot that's been in development since 2001. Unlike other walking robots which have stiff joints and a pre-planned set of movements, Dexter can dynamically adjust. It's joints are driven by air cylinders and are springy like human muscle. It has no statically stable posture which means it has to keep balancing the way a human does. And because there's no programmed walking motion, Dexter had to learn how to walk, allowing for a much wider range of walking abilities than could've been programmed. His walking is still a little stiff though, so I give it another ten years before they perfect this thing and put an Arnold Schwarzenegger skin over it.
There's another picture after the jump, as well as a video of Dexter getting pushed and learning how to walk.