Someone just asked about Mars in the WorldWind Java forum and this reminded me the imagery is out there for the .Net version of WW, begging to be streamed into WWJ.
Here are Mars MOCColorizedLayer.java and Moon Clementine40Layer.java - they are supposed to go in worldwind.layers.Mars and Moon respectively. December 13 update: get the two full globes here.
This of course is just a preview of the two bodies - over the Earth surface. The elevation data is out there too, but needs to be compressed differently for WWJ, and that is not ready yet, i believe. Eventually the Moon and Mars will have their own globes, elevation models and layer sets.