Solar and wind chargers
It doesn't get much simpler - use either the sun or the wind to charge up your favorite gadgets from the mobile phone to the laptop. My experience of these in the past has not been amazing but the technology just keeps on improving.
It seems that you can get these solar chargers in a wide variety of forms. It is now common to be able to store the power in these devices as well so your device will keep charging when the sun goes behind the clouds and also this charge will be available as extra stand by power. Some of these devices can also charge from non-florescent light to give you instant power on the move, either at work or at home. One of the things to look out for though is to make sure it comes with a wide variety of connections.
The wind chargers convert the wind into electricity via an integral wind turbine and will assist any individual on a long ride. Typically these devices will be able to charge any of your 5v gadgets and fit easily to you or your bicycle using simple connection systems.
In many cases both solar and wind chargers are chargeable from mains power as well to give them a greater flexibility
Fit for purpose
Value for money