I make an issue of batteries and I always try to share what I can see that are interesting and promising.
Now, Brother Industries from Japan has developed a battery that charges when you shake it. Called the "Vibrant Energy Cell" and they'll be showing it off at Techno-Frontier 2010 in Tokyo.
It comes in AA and AAA sizes so I suppose it works with just about anything that times these batteries. Even other chargers that use them to charge other devices.
Personally, I'm more of the solar and other renewable energy source kind of guy but if I had to buy an AA or AAA battery, and the VEC batteries work as advertised, why get anything else?
It's not going to power your laptop but it just might be enough to power an MP3 player. Image working out and you run out of juice. Shake it a bit and you get an extra 30 minutes or so, might be enough to complete the work out.
More at CNET.