The HiRISE camera onboard Mars Reconnaissance Orbiter keeps churning out incredible images of Mars. This one is very cool, but it's not obvious why at a glance:
I had to look at it for a moment to realize how amazing it is: there is a scarp (very steep and tall cliff) going across the bottom right corner, and it's the shadow of that scarp cutting across the image that suddenly gives you a sense of looking right down a cliff.
Yowza. The full view is beautiful as well.
Also, check out the boulder race on Mars! Some of my favorite images are ones that imply (or show direct evidence of) motion. Mars is still a dynamic planet.