I’m always on the lookout for interesting interface devices between the computer and the real world. Cheap is also good. I came across a nice looking mini servo controller from Pololu here: http://www.pololu.com/products/pololu/0207/.
Also, I’ve been thinking about trying out some of these too:http://www.phidgets.com/. They are input and output devices with an easy to use USB interface built in. Seems like you could create quite a few interesting things with them.