The Moon Ring by Cunicode is a topographically correct slice of Moon. Made with planetary data from a Lunar Reconnaissance Orbiter LOLA available in all sizes 3D printed on demand in Stainless Steel, with multiple finishings.
Taking scan data from an existing source such as the moon scans from the Lunar Orbiter is an interesting way to add details to a design using 3D printing that would be otherwise impossible. Others who have used geographic data to make 3D printed products in the past include TinyMtn who 3D prints, tiny mountains along with the Society for Printable Geography who make a large range of jewelry based on satellite data.
Of course you can always 3D scan existing objects with apps such as Autodesk’s 123D Catch by taking 30-40 photographs around an object which are then converted into a 3D model using photogrammetry in the cloud. You can then download the 3D model and with a little bit of editing, 3D print your 3D scan with Shapeways.