NASA is working on a helicopter drone that should explore the martian surface from the air.
It has proven to be very difficult to navigate rovers on the red planet as vision is limited by the view of onboard cameras. Images from orbiting spacecraft are currently the only support available. A low-flying drone could therefore prove to be very usefull addition.
The drone is currently still in development by NASA’s Jet Propulsion Labratory (JPL), which focuses on creating unmanned robots. The drone will not be able to fly around on its own. The idea is that the drone scannes the region around Mars rovers. Researchers will then use that (more detailed) data to better determine what spots are worth researching and plan a more efficient road along the way.
More on the subject here: http://www.jpl.nasa.gov/video/details.php?id=1355