A selection of RFID tags from Timo’s Flickr set.
You will have probably used some of them already in your daily life - Oyster cards, swipe cards, etc. (see above image). It’s an interesting cross-over of cultural and social practices and interaction, product and service design with a whole bowl of technology mixed in.
For anyone learning about or teaching interaction design and related disciplines, it’s a great resource and they have also put all their design briefs online.