by dmuren, published
This is my skull. I know it's not the first skull on Thingiverse, (see here http://www.thingiverse.com/thing:827) but I thought I'd back it up just the same, in case I needed another copy someday:)
I extracted the mesh from an MRI that I had done as part of a friend's research project at Princeton University (although I have had success getting MRIs from the doctors office too). The MRI comes as a hdr file, which is basically a stack of high dynamic range images of slices of my head. I used Osirix ( http://www.osirix-viewer.com/ ) a free, open-source viewer to read and convert the file, which I exported as an OBJ, and imported into Blender. There was a SIGNIFICANT amount of cleanup necessary, and lots of finessing of the mesh to make it watertight and manifold -- in order to reduce my work, I selected only the better half of the mesh, and mirrored it, so that's why it's erily symmetric. I swear I have a pretty normal looking head, even without editing.
Teeth proved a problem -- they have a different water content than bone, and didn't all get caught by the scan -- so I just left them out.
I also joined the mandible to the skull to facilitate printing. Otherwise, that joint gets really thin, and you would have to print out multiple parts.
I'm releasing this under a attrib, CC, share-alike license. I would love to see all kinds of weird stuff derived from it (even commercial stuff is OK) -- just drop me a line of you make something awesome!!
I don't yet own a Makerbot, so I couldn't test this puppy out, but based on the overhangs which are possible in other designs, I think the orientation I have the file in is the best chance for success. You may need to add a post between the lower and upper jaw to keep it from sagging. If you make a revised version that prints, let me know, and be sure to re-share.