Mikola Lysenko has created an app to turn an 8-Bit character sprite into a 3D printable model with his Shape Carving Editor using WebGL and the Shapeways API.  You can see some of his 8-Bit voxel sprite models in his Shapeways Store.

To use the Shape Carving Editor to make your own models take a look at Mikola's blog which has all of the instructions how to use the app along with all of the thinking behind the project.... 

The source code for the client is available on GitHub, so feel free to download it and try it out.

This is a 3D Printed mobius strip of Level 1 of Super Mario Bros. The whole level is wrapped around itself in a single surface, and poor Mario begins and ends at the same spot every time

All the elements from the level are there: every mushroom, turtle, cloud and star. They are all carved out of the surface at different heights, which looks fantastic when you have a light coming from the side, and each block casts a shadow.

It's a great piece to have on your desk, or to hang from a string to let it spin around.