QR Codes are fastly becoming very popular in education for a number of reasons but mostly because students and smartphones are becoming synonymous with one another. If you don't know what a QR Code is you should check out the Common Craft video which does a great job of explaining them in "Plain English". If you are ready to start creating your own codes for your students be sure to check out this QR Code website called QRStuff.com. On this site you can generate a QR Code out of just about anything (see image below). They will also put your code on anything you can imagine (t-shirt, hat, even a chocolate bar). If you are looking to get started using these codes in your classroom check out this collaborative slideshow of ideas for how you can incorporate QR Codes into your classroom.
If you are looking for a quick way to get some QR Codes up in your room you can use QRStuff.com to create a code which links to your class webpage or Twitter feed. Another idea would be to create a code for your students which will get them to your homework calendar quickly.