The European Space Agency news service has a story about the Mars Express mission, launched in December 2003. On November 23 it completed its 5000th orbit of Mars. The news story describes the details of the mission:
"During its mission to investigate martian mysteries, the orbiter has revolutionised our knowledge of Mars, probing every facet of the Red Planet in unprecedented detail. Some of the most visually astonishing results have been returned by the High-Resolution Stereo Camera (HRSC), which has produced breathtaking, 3D colour images of the diverse martian surface – with its giant volcanoes, sinuous valleys and ice-modified craters."
Read more at the ESA site.