Phones with a camera have a built in scanner. We recommend using Barcode Scanner on Android.
Scans both standard barcodes and qr codes, Bluetooth enabled. Comes with USB cord and cradle.
This is a fast, accurate, dedicated hand-held scanner - it plugs into the computer via USB.
Solid 1D scanner on a wireless cradle. - Reference Guide
This is a Bluetooth enabled wireless scanner that works with iPhone, Android and Chrome OS. This scanner only supports standard barcodes and will not scan QR or other 2D codes.
The guys at BarCodesInc have a lot of QR code scanners to choose from.