RFID emulator
[Alexander] built an RFID emulator. It uses a wire coil (not pictured here) and an ATmega8 to represent any tag that is EM4001 compliant. This iteration requires connection to a computer to send the tag ID information to the microcontroller. In the video after the break it looks like he's using a DIY RFID reader [...]
http://hackaday.com/2010/01/03/rfid-emulator/