This is the XBee XB24-Z7CIT-004 module from Digi. Series 2 improves on the power output and data protocol. Series 2 modules allow you to create complex mesh networks based on the XBee ZB ZigBee mesh firmware. These modules allow a very reliable and simple communication between microcontrollers, computers, systems, really anything with a serial port! Point to point and multi-point networks are supported.
These are essentially the same hardware as the older Series 2.5, but have updated firmware. They will work with Series 2.5 modules if you update the firmware through X-CTU.
This Xbee also has a chip antenna which is basically a small chip that acts as an antenna. Quick, easy, cheap, and not in the way.
Digi Part #: XB24-Z7CIT-004
Warning: Series 1 and Series 2 XBee modules have the same pin-out. However, Series 1 modules cannot communicate with Series 2 modules.