We can find out all kinds of USB scanners in the market. But if you want to scan documents via your iPad or iPad 2, apparently iConvert portable scanner should be more suitable for you.
iConvert is a portable scanner designed for both original iPad and iPad 2. As we can see from the images, an iPad dock has been integrated into the portable scanner, so you can conveniently dock your iPad on the scanner in order that the portable scanner can scan documents or images in high-resolution 300dpi into your iPad. Apart from that, the front feeder can be adjusted from 2 inches to 8-1/2 inches wide to fit many size photos and documents. And the iPad scanner also comes with a custom free app available from App Store.
iConvert portable scanner is priced at $149.99 USD. At present, Brookstone has started accepting the pre-orders of the iPad scanner. If you’re interested, jump to Brookstone online store for more details.