A High Efficiency 14W Solar Charger for $50.
http://www.amazon.com/Christmas-X-DRAGON...s=solar+chargerI have good results with NewTrent Powerpaks. This is the rugged version;
http://www.amazon.com/New-Trent-PowerPak...ywords=newtrentThis combination should also satisfy the more power hungry requirement USB devices for the larger Android and iPad tablets.