I recently completed an RFID project using an Arduino and the Parallax RFID Serial Card Reader - here are the hardware and software notes on making it all work.
1 - Arduino ( I am using an UNO R3 for this demo)
2 - Parallax RFID Serial Card Reader
3 - Solderless Breadboard
Step 1: Wiring the RFID Reader
Insert the RFID board into the solderless breadboard.
Jumper 5V to VCC on the RFID Board
Jumper GND to GND on the RFID Board
Jumper Digital IO pin 2 on the Arduino to /Enable on the RFID Board
Jumper Digital IO pin 5 on the Ardunio to SOUT on the RFID Board
If you power up the Arduino the LED on the RFID Reader should light green. In the next steps we will load the library and code to make the reader work.