SRI International and the Defense Department are developing these boots that will convert the electric power of walking into electricity that can be used to charge batteries. This sounds like a great way to use energy more efficiently:

At the heart, or rather sole, of the experimental foot-ware is a heel made of a special elastic polymer. A tiny battery positively charges one side of the flexible material and the other negatively. As the material is compressed and released — such as by the foot pressure generated during walking — the distance between the positive and negative sides change, which in turn creates electricity.