Below are some links that I have found useful or interesting related to RFID or proximity access control.
RFID Proximity Security System - Final Design Project
Arduino LF RFID Tag Spoofer
Home made PIC RFID Reader
RFIDToys Forum
RFIDiot Library
BlackHat Proximity Card Cloning Demonstration
Atmel Corporation RFID Info
Texas Instruments RFID Info
RFID Projects/Forums
Proxmark RFID Test InstrumentRFID Proximity Security System - Final Design Project
Arduino LF RFID Tag Spoofer
Home made PIC RFID Reader
RFIDToys Forum
RFIDiot Library
Videos
RFID Hacking Demo - Sacramento Capitol BuildingBlackHat Proximity Card Cloning Demonstration
RFID Vendor Information
EM Microelectronic RFID InfoAtmel Corporation RFID Info
Texas Instruments RFID Info