I really need to start using QR codes. This post has a link to a custom QR code app and many ideas of how to use them in the classroom, like having a math problem projected on the board for the kids to get.
Make your own QR code! I read an article about student work displayed in the hallway- each piece had a QR code underneath and when someone scanned it with a smart phone, it linked them directly to a video of the student explaining the assignment. How cool!