This is the very popular 2.4GHz XBee module from Digi (formally Maxstream). These modules take the 802.15.4 stack (the basis for Zigbee) and wrap it into a simple to use serial command set. 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 modules are great for working with Arduino systems and work with the built in serial port.
Now these XBees have the antenna integrated into the PCB! No more worry about bending or breaking the antenna, and you still get the same great range! These modules are Series 1, and compatible with other Series 1 Xbees (including ones with the wire-ship antenna).
We use the UartSBee to program the Xbee units, which is also used as a PC interface.