Expansion boards (shields) in the mail

One of the first things I'd like to understand is the expansion capabilities currently available for the Arduino. In the Arduino community, these snap-on boards are called "shields", and they fit directly on top of the Arduino, taking power and some IO pins from the base board and passing them through to the shield circuit.

There are a few boards out there today, so I picked up:

• Zigbee shield (from Sparkfun)

• GPS shield (from Libelium)

• USB memory stick (VDIP1 from Vinculum)

They should come in over the next few weeks, and when they do, I'll be sure to provide a write-up and take plenty of pictures. I'll try to do my best to stay on top of all the available shields on the market, as well as those "in the pipeline."