The Japanese retailer Rakuten is offering a nifty iPad case that basically transforms your tablet into a MacBook Air. The NoteBookCase for the iPad 2 features a built-in Lithium-polymer battery, USB port, mini USB port, and Bluetooth for the keyboard.
The USB ports allow you to charge the case while charging your iPad, or any other USB powered device. The iPad case should also be compatible with the new iPad since it's not much thicker than the iPad 2. The NoteBookCase is currently only available through Rakuten's Japanese website, but it could make its way to their U.S. based website Buy.com.