Arduino and RFID

Hi,

Im fairly new to arduino and i was looking around for some arduino-based solutions with RFID. I was wondering if anyone has useful hints for building an RFID reader/writer using an arduino.

The antenna has to be an open external antenna(like this one http://www.instructables.com/id/RFID-cat-door/).

Thanks in advance.

Dvds.

Most people buy them but here is how to make one.
http://playground.arduino.cc/Main/DIYRFIDReader

readymade solutions are also helpfull

Sparkfun sell them.

thank you, got any example of other projects?

How about this http://tech.nocr.at/hacking-security/howto-rfid-cat-door/