I recently bought a sunlinq set of solar panels with the idea of recharging various gadgets (GPS, MP3 player, phone, AA batteries, etc) when I was away from home and had no access to mains. The solar panels are light, flexible, waterproof and very durable they also fold down to the size of a thin book. The come with a range of of adapters including clips and a female car lighter socket which when combined with a 12v dc to 5v usb adapter can charge virtually any gadget you care to name. Unfortunately it is pretty expensive but comes in a range of sizes and costs (I went for the 12 watt one)
More info can be found here and a UK supplier can be found here.
Here are some pics: -