This pedal generator is still in the development stage. I am hoping the end result will be a 100W max generator which can be transported by bicyle. It is based upon a stand which was used to convert an ordinary bike into an exercise bike. The bike sits on rollers which spin when the wheel turns. The rollers are connected to a permament magnet generator.
This is intended as a demonstration for adults, as well as a useful 'on-site off-grid' power generator. I am hoping to rig this up to a larger sound system.
Update:
The generator was first used at the Nottingham 'Spring into Action' events. It was cycled both to and from the events (total of about 30 miles) which shows that the unit is portable. This unit seemed to be pretty efficient, easily generating about 50W and 100W if pushed.
The unit is now travelling to Gaza with the Pedal Powered Clowns.

The pedal generator folded up.

Unfolding.....

....still unfolding.....

The rollers and generator.

Close up of the generator (a motor from a skip) and the rectifier (to stop the generator motoring when connected to a battery).

....unfolded and with a bike attached.

Close up of the wheels on the roller. The stand near the pedals stops the wheel pushing down too hard on the rollers.

Campaign for Real Events Pedal generator info and organiser of the pedal power convention
VillageTech Solutions Pedal power for application in the developing world. A nice locally produced unit for home electricity.
Innovate or Die Competition for pedal powered devices run by Specialized bike company. Some amazing ideas - check the youtube links.
Pedal Powered Generator DIY plans for making your own pedal generator. US site.
MayaPedal Great Canadian/Guatemalan NGO who work on pedal powered devices for rural development.