Not entirely sure if they appeal to our environmentally-friendly side but a company called Cellboost is offering the first ever disposable battery recharger for mobile phones. As soon as your handset battery goes blink you plus the cigarette lighter style charger into the socket and you have power. Might be worth keeping a few handy in your bag for emergencies.
It has been on sale in the US for a while, but completely slipped under our radar. More here.