PowerFoot by iWalk

A completely self-contained robotic system, PowerFoot One is the culmination
of years of research in biomechanics, bio-energetics, materials science and
joint control. Two powerful microprocessors and six environmental sensors
evaluate and adjust ankle position, stiffness, damping and power thousands of
times a second. Control algorithms generate human-like force while traversing
level ground, slopes and stairs, providing active amputees with near-normal
gait and lower energy expenditure compared to state-of-the-art passive
prosthetics. 

iWalk
http://iwalkpro.com/index.html

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First Robotic Ankle Developed by Inventors at MIT

It's a breakthrough for people who need prosthetic limbs. It's the first
robotic ankle. It was developed by inventors at MIT, one of whom is a double
amputee himself. They're working on a research project in Providence and
Boston to help war veterans and others who have lost limbs. Iraq war veteran
Garth Stewart lost his left leg below the knee in an explosion and now uses a
robotic ankle. 

From and video:
http://www.myfoxboston.com/myfox/pages/Home/Detail;jsessionid=B8B53D5518575A63B3509F4352750A21?contentId=3859841&version=1&locale=EN-US&layoutCode=VSTY&pageId=1.1.1&sflg=1

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Walking the Walk to a Perfect Prosthesis - Providence Journal

In 2004, researchers at the Veterans Administration Medical Center, MIT and
Brown University formed a special group with a singular purpose: build
artificial arms and legs that perform like, if not someday better than,
biological ones. 

From:
http://www.projo.com/news/content/new_prosthesis_24_07-24-07_UL6FPQG.3271cec.html