Kentaro Fukuchi originally built this simple controller for an art installation. He needed an easy way for visitors to switch effects on an EffecTV system. To avoid writing device drivers he canabilized a cheap game pad. There were 16 available buttons but only 12 were needed. Once the rotary switch was wired to all of the buttons he could use simple scripting to grab the button press events. You could use this to control a variety of things and Kentaro gives a couple possible ideas on his site.
[thanks Jaime Wong]