Fuel cell technology gets mentioned all the time, but you'd be hard-pressed to name more than a few implementations that are commonly used today, especially by the general public. eZelleron's "Kraftwerk" could change that, with the 198g gadget apparently capable of recharging an iPhone over 10 times before it needs a quick, three-second refilling.
The Kickstarter project had a goal of $US500,000, but it's blown past that and now sits at over $US1 million, with well over three weeks left to go. The device itself promises a lot for its relatively modest $US49 price tag -- a lightweight, excessively portable (8.86 x 7.49 x 3cm) power generator that runs on gas and can charge devices via its single USB port.
The Kraftwerk can be refuelled using a typical gas cartridge, in the same manner as one would a lighter. It pumps out 5V and delivers 2W of continuous power, with a peak output of 10W, enough to satisfy almost all phones and tablets.
If you do go for the lowest tier, you'll not only get a charger, but 12 cartridges of LPG. I'm not sure what the import restrictions are on butane / propane (if any), so you might want to look that one up.