Updated June 12/2011
Added schematic and board images, and provided the Eagle files.
The latest revision of the "Dual LED matrix shield" is shown in the photos below.
This board is a bit longer so that it can be fitted with standoffs on both sides.
It also features an on-board tilt switch (white cylinder in the photo above), two push buttons and an infrared receiver.
The two RG (Red, Green, Yellow) LED matrices are inserted in the machined headers (round pins), after the components are soldered to the board.
The schematic and board (also available as Eagle files here and here, respectively) are shown in the images below.
(Click on the image to get a bigger size.)