Highly Recommended Reading : QR Codes in the Classroom - includes Implementation tips, a real look at problems and how to deal with them and some great, realistic ideas for using QR Codes.
QR Treasure Hunt Generator - Generate a QR code-based treasure hunt!
Periodic Table of Videos - Rather than a list of long URL's, this graphic shows a different means to providing video links using QR codes.
See it, Say it, Scan It - for younger classes- Students look at a picture, say the word, and scan the QR code to check their answer. See an example (with many other variations)
Develop a content rich resume - could also use to provide links on a paper-based resume. Carefully consider that QR codes are only used on paper, so this wouldn't be cool on a digital resume when a link would work much more easily.
Mystery Math - Students receive codes, scan, work the problem (and for an extra step, include a code to check their answer!)

Create a QR code based activity for your classroom