I've had a couple of cheap solar chargers and they were pretty useless, refusing to charge unless they were in direct sunlight and then taking hours and hours to recharge themselves.
I have considered spending more money on a "premium" product such as a Powermonkey, but the independant reviews I've Googled are a pretty mixed bag. Again, seems to work ok if in bright sunlight for several hours, but if it's cloudy then there just isn't enough light to charge it effectively.
The alternative I'm currently looking at is a high capacity powerbank such as this one from EC Technology
link. I normally go camping/touring for a max of 4 or 5 days at a time, and this would have more than enough power to keep my devices going for that time. If I needed it for longer, then I could use powerpoints in cafes/campsites etc to give it a boost whilst on the road.
Depends where you're think of going really. If it's the UK, then you can't realistically rely on the weather.