RedLaser (Appstore Link) is an amazingly reliable iPhone app to scan barcodes and search the web for the matching product.
It is probably most useful to U.S. customers since the product search is customized for the American market. However, there is a hack which can implement the following use case in a bookstore:
To implement this use case you have to buy the RedLaser app and then go to the following URL on the iPhone:
http://www.redlaser.com/CustomApp.aspx?name=Amazon.de& url=http%3a%2f%2fwww.amazon.de%2fgp%2faw%2fs%2f%3f__mk_de_DE %3d%25C5M%25C5Z%25D5%25D1¶m=k&imageurl=http://www.redlaser.com /data/amazon.png
Follow the instructions to install a new icon on your homescreen and you are set to go.
This hack takes advantage of the method described on http://redlaser.com/apps.