One of my bikes has a bottle dynamo that presses on the tire and powers the front lamp. The Siva Cycle Atom is a modern-day equivalent, only it won’t rub away your tire or slow you down, and it’ll charge your gadgets instead of just running your lights.
The Atom, another Kickstarter project, attaches to the axle of your rear wheel and turns the wheel;s movement into electricity. It outputs a standard, smooth 5v at 500mA, the same as a USB charger, so you can hook it up to anything you need to charge. There’s also a removable battery that you can take with you when you lock up your bike.
Uses? The iPhone is the obvious one, letting your use it as a GPS without running down the battery. But you can also charge bike lights, or a real bike GPS like the Garmin series of bike computers, or even a Bluetooth speaker for unlimited in-ride music.
For city use the $105 widget mightn’t be so useful (except in San Francisco where people trade in perfectly good old cars for a Brand new Prius just to be “green”), but on a long bike trip this kind of thing is what lets you stay independent for longer.