Use some lasers to write on the wall!
8 laser leds (you can buy them for 4 euros here).
two-coil stepper motor
4 power NPN transistors, 4 power PNP transistors, 8 1k resistors. Wires
Step 1: Build a Controller for the Stepper Motor
Build a dual H bridge, using the above schematics, which I obtained from here. (Thanks Kerry Wong!)
Step 2: Attach the Lasers to a Support and Wire Them to the Arduino
Connect 8 of the lasers to the arduino (1 i/o pin for each laser) and fix them to something solid (I used a scrap PCB).
Step 3: Paste a Mirror to the Motor
Mount everything on some support (I used an old ethernet switch).
Step 5: Write the Code.
Here is the code I used. At the very least you should assign the correct pins you used to connect the lasers and the hbridge.