These ideas are still swirling around in my head and aren't fully thought out, so any thoughts are appreciated:

Body of Music
An instrument that captures your body as a tone and can then be manipulated by gestures. Using OpenCV, each blob would be visualized on a screen in front of the person. The tone for each blob would be calculated by its size, shape and position. As a person moved their hands, they could slice and push their body around the screen to generate new tones.

Mechanical Pencil
A small robot would receive commands through a terminal and interpret them with a pencil on a canvas. The idea is that you would have a real life person giving commands to a machine and the machine would be manipulating the real world. The inspiration for this is the Yellow Drum Machine.

Automatic Event Planner
Using calendars from social networks, the application would figure out when you and your friends are available. Based on your preferences, the application would add the event to your calendar and purchase tickets if necessary. The idea is pretty similar to iLike's feature where you can click on a band that you "want to see" except this would go a step further and actually set everything up for you.