A recent .STL upload to the Thingiverse model repository does just that. It's a 3D model of an actual human brain!
Now before you speculate on exactly *how* Jordan Miller obtained this anatomical wonder, we have to tell you that the caper was entirely legit:
This is a human brain I extracted from a public domain MRI dataset from Slicer3.4.
Commenter Zach echoes our immediate urge: "OMG. Must print!"
We're considering what other body parts might be printable from publicly available datasets? Erm. Oh, never mind...