Folks seem to really like this product on Amazon.

Before buying this, however, I'd suggest looking at a competing product from Satechi. I couldn't find dimensions for the Anker, but the Satechi looks to be similarly thin and similarly sized.

http://www.satechi.net/index.php/cel...energy-station

It is more than twice as expensive, but also provides a 10,000mAh battery (rather than the Anker's 3,200) at what appears to be a similar weight.