The Camera Culture Group at MIT Media Lab will be demonstrating a barcode replacement at Siggraph 2009 in New Orleans next week. Called Bokode they consist of an LED under a mask and lens. Information is encoded in the light shining through the mask which varies in brightness depending on the angle it is seen from and can be read by a standard mobile phone camera. (Video below).
Added 12 December, 2010: Bokode: Imperceptible visual tags for camera based interaction from a distance. (pdf)