Smart cards are standardized plastic (or sometimes paper) cards that contain a chip. You see them a lot these days, to be used for riding public transport, buying things from vending machines, borrowing books from the library, gaining access to buildings, and lots more. They are interesting to look at, because they often include very low power circuits, and special features to prevent tampering.

• Chipknip
  A smart card based payment system from the Netherlands.
• OV-Chipkaart
  Another Dutch smart card: an RFID card to be used in public transport.