The page I wrote on 3D printing has proved to be pretty popular so I thought I'd mention that the NIH 3D print exchange has been updated with new features to improve printability.

AstroPrint is a neat way to slice, store, and manage your print files in the cloud. The service works by taking your uploaded 3D model, adding supports, slicing it, and saving the gcode in your account online. You can then access, download, and print your models. It's like a combination of 3D printing software, such as Cura or Repetier Host, with cloud storage.

and

A cloud-based 3D mesh repair application from Netfabb. Sometimes the mesh of a model can contain errors that are hard to find, and even more difficult to fix. Holes, inverted normals, intersecting faces, and isolated pieces can all cause problems during 3D printing. These mistakes can occur frequently when models are generated from "messy" datasets, such as image stacks or CT data.