A Boy Scout’s Guide To Navigation Skills (link provided by a Boy Scout who appreciated the previously posted information)
Geocaching Resources – Mapping and QR Code Scanning
Google Maps – Google Play Store
QR Droid Scanner – Google Play Store
Update: The standard “Camera” App in recent versions of iOS for the Apple iPhone supports QR code scanning. I believe that the same applies for Android, but I do not have an Android phone, so I cannot verify that first hand.