In discussion with my gaming buddies this moon-scape map (MoonQ20, for all you Gamers out there) was selected for as the next attempt.
There are several problems with machining these maps. Sharp changes in elevation, ie. cliffs, cause the most trouble. If I don't take this into account (and I am discovering that I am a "learn from hard experience kind of guy") then the machine crashes into the cliff and messes the whole carving up. My bits can only accommodate an inch, so I have to plan around the places where it needs to carve deeper than that.
I want this to be a coffee table with glass over the carving...and if I am feeling really ambitious then I'd like to paint this a gray (with a hint of blue) and speckle it with some black atop the "ridges".