After sorta-kinda hacking together one RFID-based project, Benjamin Eckel decided that enough was enough, and went through the effort of documenting the process correctly. If you’ve got a Parallax RFID reader and an Arduino kicking around that you have been meaning to hook up, this looks like a good place to start. He includes both the source code and some nice tricks to overcome some of the limitations of the system that he has run into.
[photo by Flick user todbot]
In the Maker Shed: