The six legged RHex Robot, from the makers of BigDog is designed for extreme terrain. It can seemingly go anywhere. Stairs, over rocks, through mud, swim through water, run through fields... If it gets stuck it just goes crazy until it's moving again. Kinda cute too. At least until hoards of them begin marching from our desktop fabricators only to be turned into zombies by the latest botnet.
See the video links.