I've been doing quite a bit of parts with Shapeways lately both flow models and functional parts. One of the latest is a rework of my servo actuated plug valve.
Two parts allow a Swage-Lok SS-4P4T valve to be actuated by a Hitec servo - I recommend a high torque metal gear model like the HS-7954SH. The only other hardware required are (you'll need taps to clean up the threads in the nylon):
qty 4 8-32 x 5/16" Socket Head Cap Screws, McMaster-Carr 92196A191
qty 2 4-40 x 1.25" Socket Head Cap Screws, McMaster-Carr 92196A302
The printed parts are available on Shapeways