Rugged Circuits would like to announce the Quick Shield, our latest shield for the Arduino Duemilanove and Mega (and compatible boards). This picture shows the Quick Shield itself (two PCB's) as well as the Quick Shield mounted to an Arduino Mega.
The Quick Shield breaks out all 28 connection pins on a Duemilanove to quick-connect terminals accepting bare wire from 20AWG to 24AWG. No tools are required -- just push, insert wire, and release. Another shield can be plugged in on top of the stacking socket headers, like this:
Please see the full product page for more details.
The Quick Shield is $9.95 and ships as a kit (soldering required), or $12.95 pre-assembled.