An iPhone case that has a hand-operated 500mA charger. Turn the crank for a minute and you get 40mins. of battery life for your phone. It also has a USB charging port for other devices. A charger-only variant (no case) is also available.
Crowdfunded projects pose a degree of risk for buyers, so be sure to do your research and fully read the seller's detailed description and production plans before plunking down your hard-earned money.