RFID Reader

I am working on a project with the Arduino Yun which will have a barcode and rfid reader. I already have the barcode scanner which works fine, any suggestions for an active RFID reader (has to be active) that has been used with an Arduino before?

Thanks

Maybe this page helps: (German page) Liste aller NFC/RFID Evalboards / Arduino Shields Liste aller NFC/RFID Evalboards / Arduino Shields | Regnerischer Nachmittag