The AMP-Foot 2.0

A Powered Transtibial Prosthesis That Mimics Intact Ankle Behavior (Video)
Here's a robot video that I found interesting:

The main idea behind the AMP-Foot 2.0 is to have the actuator work longer with a lower power rating while the produced energy is stored in elastic elements and released when needed for propulsion. The device is designed to provide 100% of push-off for a 75 kg subject walking at normal cadence on ground level.
Source From: http://mech.vub.ac.be/multibody/research_topics.htm