Make your own custom QR codes with this handy and free app. This version allows for zooming in on the code or changing it's size for resolution purposes. You can save your codes by pressing the "home" and "power" buttons at the same time. This will save a screen shot to your pictures folder, or use your codes on-screen.

QRCode commonly used in Japan. It is that its much high density encoding than standard bar codes and allows higher amount of data to be stored, with error correction in cases when parts of the bar code gets damaged or blocked (ie. when dirt and grease covers it).