Powerfilm makes a charger that charges two AAs and has a USB output. I used it a few times. On a sunny day it takes less than 4h to charge an iPhone, less for an iPod (won't charge an iPad). And it folds into a small package the size of a wallet. It seems to out of stock everywhere I look so I can provide a working link.
I'm thinking about getting another one that has more power and charges 4x AAs, no USB though. They cost around $100 in the US.
Both of them have charge stabilizers built-in and battery cages so they're ready to go out of the box. They also make more powerful - and more expensive - foldable chargers up to 60W that come with a barrel connector (like the 12v car cigarette lighter) that is compatible with car chargers. So you can plug any car charger to it.