DX XIAOMI Genuine 10400mAh Power Bank

This looks like a good find; http://www.dx.com/p/xiaomi-10400mah-usb-mobile-power-source-bank-w-4-led-indicators-silver-white-311565#.U4ya3Hl53UY

The benefit of this power bank is that it can do charging, whilst it is also being charged. For usage with a solar panel this means that the battery bank itself can be left on the solar panel and charge whenever solar power is available, yet you can continue to charge other devices in the mean-time.

You can then make maximum use of the available solar power, without being limited to just charging devices at night whilst the battery pack isn't charging.