A big buzzing 4-legged robot.
In separate trials, BigDog runs at 4 mph, climbs slopes up to 35 degrees, walks across rubble, and carries a 340 lb load.
If you care about robotic movement and balance, the video is totally great. (via my dad.)
EDIT: In the comments, Brian pointed out that this has come up before. In my defense, I was the first to link directly to the company's website. (The prosecution, though, is correct in its assertion that I am a moron.)
bostondynamics.com/content/sec.ph...