A small (~80mmx80mm) print of the Valles Marinaris region on Mars. You can make your own (if you aren't afraid of the terminal) by using png23d and freeware like MeshLab. png23d takes a greyscale image (like the one I posted, which shows actual topographic data from the MOLA instrument) and assigns different heights based on the pixel greyscale value. Porting the resultant solid to MeshLab allows you to reduce the number of facets to something more reasonable (like 100,000). I'm still working on the process in my spare time and haven't quite worked out the bugs...
I didn't generate this stl - I found it at this site: http://nasa3d.arc.nasa.gov/detail/valles-marineris
From the nasa website:
"This STL file is a topographic model of a portion of Valles Marineris with vertical exageration, derived from data collected by the MOLA altimeter onboard NASA's Mars Global Surveyor mission. Printed at its default size (8cm across) this model cover an area approximately 1000km across at a scale of 12.5 million to one ( 1 cm = 125 km ) Data Credit : NASA/MOLA Science Team"
Because I snagged the stl file from a NASA site, I'm giving this a Public Domain Dedication. If that makes anyone unhappy, please let me know. Keep in mind I'm just posting this to Thingiverse after trying it out! All the credit for making it is NASA's.
The Gale Crater thing I cited as an inspiration was created in this fashion.