I bought one of these a couple of weeks ago to charge my iPhone 3G on the go.
Its a portable battery that will charge any device with a USB connector or cable whilst you are on the go - excellent for long plane journeys (or days stuck in the channel tunnel).
I can happily report that it works excellently and I can now use my iPhone to watch Video on the Manchester to London train (and back) and use it all day as well.
You should be able to charge any USB device (I've just bought another for a friend with a Flip video camera)
It comes with an international USB charger with interchangeable plugs and a nice pouch.
Its approx £29 at most places - so £9.99 delivered is an excellent deal (I think).