This is what an Arduino Duemilanove (yes, I had to look) looks like.  Very simple, but also very, very powerful.

This is the Arduino with the Screw Shields installed.  This gives easy access to all the Arduino I/O pins via screw terminal.  SparkFun now has a new version that looks more like a traditional Arduino Shield.  See ScrewShield 1.5 for more information.

Now I've added the first of two Centipede Shields.  This Shield provides 64 channels of digital I/O.  You can use two of these on one Arduino.

...and here's the second Centipede Shield.  I've not set the address jumper on this one, it's just set up for the pictures. :)

Last but not least, we attach the MUX Shield to the top of the stack.  The MUX Shield will provide 48 channels of analog or digital input or digital output.  You can learn more about the MUX Shield from those wonderful digital crack sellers at SparkFun.

Even with all this stacked up, the whole thing is still under 5" high.

More later!