I built this as a project a while back, but with Adafruit's encouragement, I brought it to market as a product. Adafruit will be selling them, too.
http://nootropicdesign.com/matrixbackpack/
If you have a large RGB LED panel, you know how the wiring can become a real rat's nest. This tiny board snaps onto the back of the Adafruit 16x32 RGB panel to eliminate the mess. The ATmega328 comes preloaded with a nice animation, and it's easy to control the panel with Adafruit's library.
If you have the Adafruit panel, this is a must-have! Easy-to assemble kit, and also available pre-assembled. All the product info is here: RGB Matrix Backpack