You generate a tremendous amount of energy as you pump the pedals on a bike to get from point A to point B. That energy can now be easily harnessed to charge your small electronics with the BikeCharge dynamo.
Similar devices have existed for years and are typically only used to power a headlight on a bike. But in addition to keeping a small LED light aglow, the $US100 BikeCharge has two USB ports that provide three watts of 5V DC power to your devices as long as you're maintaining a speed of around 20km/h.
To completely charge something like a mobile phone you will need to ride for at least a couple of hours, but even short trips should help extend your phone's battery life over a day. If you find a way to connect the dynamo to an electric drivetrain motor, you just might have the world's first perpetual motion machine, right?