I have used solar chargers. I can't remember the exact one but Power Monkey is a good brand. I paid £70 for one that had a built in battery to store a charge, double solar panel, USB charging socket and adapter lead so you can charge the battery from the mains in a few hours, or took two full days of sunlight. About the size of a small pencil case. Can fully charge an iPhone from flat. I'll try and dig out the name. Used it on a remote, self sufficient four week expedition with no problems.
I've just a got car charger for going abroad (will be moving around a bit for a week), are you not happy with yours? I've read a couple of mobile forums (searching for info I cam across them) that said about some the newer phone batteries not only last longer, but charge faster as a well. I've got a new 2450mah one going from Hong Kong as I was guessing the charge time needed in the car is a bit more then 30 minutes!
Another vote for Power Monkey, also on the Gadget Show this week they had a couple of billy cans with usb sockets to charge up your goodies in the ulu. Don't ask me how it works i wasn't in the REME, mind you doubt they would know either!!