On of our students is really good with solid works - the CAD program used at the University of Paderborn. He created a transmission gear to take part in a competition. Every year the students of the University of Paderborn are asked to take part in a competition called Ferchau Förderpreis. Away from that he decided to create a 3D printable version - that looks just awesome!
In the pictures you can see two versions. The one on the right hand side is the full 3D-Version - the one in the left hand side has been stopped at 50%. In this way you can see the inner structure.