We have seen the BioLogic FreeCharge (renamed ReeCharge) that charges a 1600 mAh Lithium Polymer battery while you pedal your bike. Now there is another competitor, High Tide (a California company) is making a bolt on bike charger called the RollerGen.
The RollerGen can make as much as 30 watts of power while you pedal your bicycle. The power is stored in a small battery that sits next to the generator. The full rack (PowerRack) system even has a storage box to put your electric gadgets while they charge. The only downside, as far as I can tell, is the hefty $495 price tag. Once we get our hands on RollerGen we will provide a full review and let you know if parting with $495 makes sense.