I have a PowerMonkey 'Extreme'. It charges ok, even in low levels of cloud. It can take a while, but then a while is better than no power at all. I use it for iPhone/general phone use but also with battery charging on expedition. It will charge them on a USB charger over a day. AGain not great but better than solar used to be, and better than nothing. 'Goal Zero', an american make, are quite good too, but their kit is a little heavier. Their rough equivalent to the power monkey extreme is the 'Guide 10'.
http://www.goalzero.com/shop/p/79/Guide ... e-Kit/1:1/
Again quite good. The novel thing about that one is the batteries come in a 'recharge pack' and can be used in that to power various things, but can also be taken out and used in devices that need AA. There is an adapter you can get too so that it will do AAA.
The 'freeloader' chargers that have been around or a while and are generally in places like 'Cotwolds Outdoor' are a bit shocking from experience, in that they generally a poor performing.