Wired magazine is showcasing the best photos taken during the past 5 years by the UA-HiRise camera on the Mars Reconnaissance Observer. MRO went into orbit on March 10, 2006 and has returned over 70,000 images. All of the top 10 images are amazing.
[right, "veiny gullies trace the walls of a large pit in Mars' southern hemisphere in this image, captured Aug. 5, 2007. The gullies may have been carved by liquid water millions of years ago, when Mars was warmer and wetter." Credit, NASA/JPL/UA. Caption from Wired]