Rob Walker had a piece in the Sunday New York Times Consumed column on some innovative use of QR Codes. True to form, the Times did not see fit to provide any links in the column, perhaps figuring that most readers would be reading the Dead Tree Edition. So here is some additional information to get you started.
The QR code is a two-dimensional bar code invented by Denso Wave Incorporated in Japan for tracking industrial parts. It has now caught on in Japan as part of a mobile phone application that can read the bar codes from any object, such as a billboard or article of clothing. The image can contain up to 2,953 bytes of binary data, although the usual use is to encode an alphanumeric string or a URL.
There is almost no limit on where a QR code can be displayed except that it needs to be on a light background. An Add to Friends application for Facebook lets you order a T-Shirt or tote bag that when scanned by a cell phone gives the URL of your mobile Facebook page. TOCA ME GmbH in Munich runs emma cott which will do the same thing for Facebook, Twitter, MySpace and nine other sites. John Young makes needlepoint pillows. Lendorff.Kaywa sells a scarf for £32.50 decorated with Space Invaders sprites and a bar code that reads "Insert coin for extra life." There's even a Flickr stream of QR Codes in the wild.
Semapedia encourages people to print out stickers of Wikipedia URLs and apply them to relevant places in the real world.
There's lots of useful stuff on the Kaywa site, including a QR Reader (some phones such as the N95 are shipped with one) and a QR Generator so you can make your own codes. Japan Marketing News found this TV ad from NTT DoCoMo illustrating a billboard application.