The Amazing Frisbee Black Box or BASIC Stamp Frisbee
Make an ultralight, easy-to-assemble, acceleration recorder that you can use to measure the dynamics of small vehicles.
Be the envy of your colleagues with this über-nerd coffee mug that generates power from heat using the same energy converters that are used on deep space probes! Equipping a mug with thermoelectric energy converters and heatsinks will allow you to drive a small motor or other electrical device. You can even claim to be environmentally responsible by extracting useful work out of heat that would otherwise just go to waste.