I modified the tweaked version by Ulf of the Dart Vader helmet to make a key chain out of it. If you check the original mesh you will see a lot of misplaced vertices and weird edges and faces. I tried to correct some of them and also a handle for the chain, a hollow space inside to save material and I scaled the model by a 10% to make it a bit smaller. It prints quite well on a Makerbot with plastruder mk5 and abs plastic with the default skeinforge settings.