Bryan Jacobs of Knick Knack Sound built PhOut12, a motor shield controlled through USB-MIDI.

The PhOut12 allows software traditionally used for music to control motors.  The board can control up to 12 DC motors, solenoids, or relays, and up to four servos.  It also has a couple of inputs for sensors, pedals, or knobs.  This versatile board offers a lot of options for adding sound control to your art project.

Code and schematics are available at Bryan Jacobs Music.

You can purchase a kit of parts of fully assembled board on Tindie.