BeeTagg (Free) – The BeeTagg QR Reader for Windows Phone 7 can read QR Codes, BeeTagg Codes and Datamatrix. It supports the following formats: vCard, meCard, vEvent, Geo, Phone, SMS, Text
NeoReader (Free) – This is one of the best readers on the iPhone and is now on Windows Phone 7. It supports almost all types of bar codes including Data Matrix, QR codes, Aztec Codes, EAN, UPC, and Code 128.
Quickmark (Free) – Same as the iPhone app however on Android and best of all, FREE. Reads Quick Code, QR code, UPC and Data Matrix.