The Mars rovers are now going on 6 years of crawling around the Martian surface looking for evidence of life. Of the two, Spirit has had the toughest time of it, losing the use of one of it's six wheels forcing it to continue its trek backwards since 2006. In April it got stuck again, and scientists have been working on figuring out how to extricate the robot from some soft sand around a small crater ever since. There has been some good to come out of the ordeal as Spirit's spinning wheels have revealed more evidence of the past presence of water and conditions that might have supported life. More information about the findings can be read in this more recent article at Physorg.
Originally designed for a 3 month trek, the little robots that put the term 'remote controlled' into cosmic perspective have proven very sturdy and well designed providing a number of interesting discoveries over the years. I've been following the rovers' trek since they were just being planned and was lucky enough to catch a great lecture at Stony Brook 3 years ago given by one of the members of the Rover science team, but a quick look back through the posts on this site reveals that I never wrote about that, and have only mentioned the other rover (Opportunity) once. [edit: oops, make that twice]