By any measure, the Mars Rover Mission is a resounding success. Initially the pair of robots were designed by NASA for a short run, 90 Mars days, but they have lasted many times their projected lifetimes. It is now 2011 and the rovers landed in 2007.
Unfortunately, Spirit's voice went silent last year but Opportunity's status is much better. It's solar panels are key to its success because without power the robots stop working. Of course, mobility helps too. Opportunity is still mobile whereas Spirit got stuck.
As robots go these days, the two rovers are rugged but relatively simple. They are autonomous primarily because of the long radio delay that would prevent reasonable real time remote control. The robots are under constant monitoring by NASA but actions are planned and sent to the robots that would then execute the plans.
Rovers are not the only thing making a long run these days. VStone's Robot Marathon recently ran five humanoid robots on a 26-mile (42km) racein Osaka, Japan. The 423 laps took four days with one robot dropping out early. It was a neck-and-neck finish for the first two robots across the finish line. The third and fourth place winners did not finish the race but did complete hundreds of laps.
A nice overview can be found at I-Programmer's website. These were not quite the Engergizer bunny though. The human counterparts could change the robots' batteries and even motors. On the other hand, the robots had to get up if they fell down. They could bump into each other as their sensors were somewhat limited.