Shapeways is an interesting site, if you can design it on a computer they can print it in 3d. This video shows how to make a 3D printed QR code ® stamp, that can stamp anywhere and people can scan the stamp and will be directed to a website.
Check out the Shapeways Art and Jewelry categories, not much about QR Codes ®, just some very interesting work! The site even provides tutorials on how to create using 3D printing. If you want to experiment with 3D modeling on the computer check out Google’s SketchUP software.
Source: Shapeways blog