Remember BigDog from Boston Dynamics? This AlphaDog Proto is actually an improved version of BigDog and quieter. It is still a Prototype and expected to be completed in 2012.
This AlphaDog can carry a heavier load (400 lbs) than BigDog and as mentioned, it is quieter. The capabilities of this robot are to carry 400 lbs of payload on 20-mile missions in rough terrain. It is being developed by Boston Dynamics with funding from DARPA and the US Marine Corps. Here is the video.