Ask any serious bike racer, and they'll tell you that a bike needs to be as stiff as possible to avoid wasting energy. That fine for hard core racers, but most of us want our rides to be comfortable too, so we buy bikes with a nice cushy seat, and a springy suspension system to help smooth out the bumps.
Designer Deco Goodman decided that there must be a way to harness that wasted movement, so he developed the Commuter Cyclist's Sustainable Energy Source. Attached to the seat post, this device harnesses movements in the seat post spring, along with energy produced by the brakes and a wheel mounted generator system, to deliver an electrical charge that powers a headlight and built in tail light. It also charges a battery which can then be used to juice up your cellphone, or top off your iPod so you have some tunes for the ride home.
This looks a whole lot more practical that some bike mounted wind generators we've seen.