If you are looking up any number of ISBN's regularly, you should be using a barcode scanner. Instead of typing in ISBNs by hand, a barcode scanner allows you to quickly scan a barcode in a fraction of a second. It doesn't sound like much, but once you've used a barcode scanner, you'll consider it one of the best investments you've ever made.
We've personally used both of these types of barcode scanners for quite some time. Both work well, but the laser scanner will be faster with a large number of books due to its hands-free mode