QR (Quick Response) codes are two-dimensional bar codes that can be read by smartphones with cameras. They look like a Rorschach ink-blot test when you first see them. QR codes have become more common in magazines and catalogs to point people to sites for more information. Rather than having to remember and retype a URL, you can simply scan the QR code with your phone and go directly to the site.
I love this article by Mashable on creative QR codes. Companies are starting to get very innovative in making these codes look more like art and less like an eye-test. Just look at this QR code made from M&M candies from QR Arts!