There are a number of autonomous vehicles entered in DARPA's "Grand Challenge" race:
"The 2005 DARPA Grand Challenge will be held on October 8, 2005 in the desert Southwest. The team that develops an autonomous ground vehicle that finishes the designated route most quickly within 10 hours will receive $2 million. The route will be no more than 175 miles over desert terrain featuring natural and man-made obstacles. The exact route will not be revealed until two hours before the event begins."
But the one which interests me most is not some overgrown hummer, it is this little guy. By using a motorcycle rather than a 4 wheel platform it gives up inherent stability in exchange for a narrow profile. You can see more about the project here.
