If you want to charge your gadgets while you ride your bike, then the best way has been to think ahead and get the bike fitted with a dynamo hub when you buy it. Now, there's another option: a seat-post-mounted solar panel.
It's called the SolarCycle Delux, and it comprises an aluminum rack along with the solar panel itself and a 6700mAh battery with a USB port. You clamp the rack to your seat-post, clip in the solar charger (the main unit is removable for security) and hook up a gadget. If you're making heavy use of GPS then you can run the phone from the charger as you go, or just wait until you get to camp and charge from the freshly filled battery.
The SolarCycle also acts as a back-up battery, and lets you charge it from the mains, or even a hub dynamo.
Currently the SolarCycle is seeking funding on Kickstarter and the maker – Isaac Porras – wants $90,000 to get things started. The minimum pledge to get a SolarCycle panel is $150, which is cheaper than getting your wheel rebuilt with a dynamo hub inside. The full Delux kit, with battery and USB ports, is $400.
Solarcycle Delux - Bicycle USB Solar Charger Power Station [Kickstarter via Bike Snob]
