CES 2013 - Antec Mobile Products (a.m.p) debuted the PowerUp line of products at CES 2013. These on-the-go cell phone chargers are rechargeable batteries that can charge a wide variety of mobile products. Really anything that charges through USB is supported. A cool feature is that the battery itself charges off of mini USB, so the same charger can then be flipped around to charge your device.
The PowerUp battery packs are available in three sizes: 2,200mAh, 3,000mAh, and 6,000mAh. a.m.p also has the Hub Charge product, which features four USB ports.