Decode Camera is developed by ioshack with a price tag of $1.50. It is compatible with iPad and supports the front and rear facing cameras. iOS 5 and 6 are supported as well.
NativeQR is similar, but features a $1.99 price tag. It lacks iOS 5 and iPad compatibility, but iPad support will be soon released. Developed by Evan Swick, NativeQR is also integrated with your contacts -- allowing you to quickly share your information via a QR code.
You can find both tweaks in the Cydia store. Let us know which you one prefer!
Decode Camera [$1.50]