It turns out that its relatively easy to power a Pi via cycling. You simply require a Dynamo and the appropriate kit. Whilst this is not a cheap way to power it and will require plenty of pedal power it is very environmentally friendly and enables people to use computers where otherwise it would not be possible.
This is one aspect of the Raspberry Pi that makes it very suitable for use in places where you would not normally put a computer. If you are interested in using a Bicycle to power electronics you can find out more at: http://www.pedalpower.com.au/
Imagine where computers could go and you would not have to worry about the power. Of course another way to power it is with a Wind up mechanism and these can be bought for less than a tenner! Amazon.co.uk