The wind-blown dunes of Mars
The HiRise Camera on Mars Reconnaissance Orbiter has released some wonderful new pictures, showing what are called barchan dunes on Mars.
Barchans are crescent-shaped, with the horns of the crescents pointing downwind. One barchan is visible in the upper part of the image, with the Southeast (lower right) horns longer than the other. This trend, along with the position of the steep face of the dune on the South side, indicates that the predominant winds which formed the dunes came from the North.
There are a lot more great images on the websites above.