RFID522
An easy to use arduino library for the RC522 rfid reader.
Convert it into a rfid reader/writer for your computer
In the examples directory you can found the ReaderFirmware sketch. This sketch converts your arduino + RC522 into a rfid reader/writer device (over serial port).
You can also attach an hc-05 for a wirless rfid reader (I use it to have an rfid reader in my android phone using the java library)
Build a device like that is very cheap (about 7€ arduino mini pro + serial to usb + RC522), very small and hightly customizable (you can create your own primitives since you control the firwmare!).
Libraries available
When uploading the ReaderFirmware sketch you can use it as a RFID reader connected to your computer in the following languagues: