I'd encourage you to think again about electricity-based gadgets. Think of your audience, the most electronics-savvy generation in history.
Bike-powered washing machine Also
here
Bike-powered movie projector
Bike-powered laptop
Bike-powered golfing
Bike-powered music concert
Bike powered (velo)taxi/tuk tuk
Bike-powered gravity simulator
Bike-powered water pump
Bike-powered generator
Bike-powered locomotive
Bike-powered welding
Bike-powered cellphone charger
Bike-powered bus
Bike-powered plane
Bike-powered wifi web access
Bike-powered VoIP internet telephony
Bike-powered knife sharpener
Well, there's enough to get you started. With the right interfaces, you can drive all sorts of mechanical items. With the right wiring, you can drive all kinds of electrical devices. Imagine several bikes linked to generators so you could play Rock Band with youyr buddies.
