I haven't used a USB barcode scanner before, and it’s quite difficult to recommend one if I haven’t used any, but I found some information that you might find interesting:
- Connecting barcode scanner to Arduino using USB Host Shield « Circuits@Home
- Barcode scanner from USB to arduino.. no shield
The links above are about Arduino projects with USB barcode scanners. There are some sample codes and hints to choose the USB barcode scanner. As I said, I haven't used a USB barcode scanner, and I'm not sure if the codes shared in the links above work with Galileo, but hopefully they do. You can check them and try to use them with your board.
I hope you find this information useful.