QR Codes are something I've had a bit of a play with but have not quite worked out how I would use them in the classroom. Mind you this post from Joe Dale has some great ideas. I have, however, used them as part of the corridor display outside the classroom. The aim is to change the theme of the display a couple of times a term but...
Last term's theme was 'Sakura' (cherry blossoms in Japan). I generally have a flickr image collage and some simple signs or words in Japanese but this time I included some QR codes that directed students to websites or videos that explained more about the images or the Japanese words. One code led to a popular Japanese song with 'sakura' in the title and another led to an explanation of 'sakura zensen', which can somewhat loosley be translated as the 'cherry blossom front'. The results are below, though apologies for the quality of the mages. If you're looking for a site to create the QR codes, I used Kaywa which enables you to link to a URL or shows text.