I wandered into an interesting idea yesterday. It would be really simple to build an electric generator starting from a bicycle and an appropriate generator/motor. Remember that electric motors can also be generators with a little reconfiguration.
I've done some yahoogling and found several websites and videos showing others who've had the same idea. Some of them are mechanical power systems rather than generating electrical power.
The information is linked here: http://www.7gen.com/website-categories/bicycle-pedal-generator
The most interesting thing is how these designs are kind of the opposite of what we typically do, and how the skills we have from electric bicycles could be repurposed.
Here's a few highlights:-