What app do you recommend to scan q-codes?

There are a number of apps that work well and are available on multiple platforms for free.  Google Goggles is an excellent tool that enables “visual search” including q-codes.  ScanLife supports a number of mobile platforms and recognizes multiple types of barcodes. i-nigma and RedLaser are a couple of other popular options.  Any app that can scan a QR code will work.  The app store for you phone will have a number of options.