This is a simple to use, USB to serial base unit for the XBee line.
So you have a few XBee modules. Cool. Notice that they're not that easy to breadboard and experiment with?
Here's your solution! The SparkFun XBee Explorer USB module. Stick your XBee module in, then stick your USB cable in, then connect it to your PC. DONE. Well, you might want the X-CTU software to play with it to access the serial and programming pins, but it's pretty much that easy!
Note: XBee modules and USB cable sold separately