Peggy: Like Lite-Brite with LEDs Answered
Evil Mad Scientist has been really putting out the LED projects lately. They were selling a Mooninite kit, then they had pink LEDs (yum), and now they have info on how to make Peggy, an LED display where you simply plug them in and watch them glow. This 25 x 25 grid allows you to worry about what image you want to glow instead of how they're going to be wired up.
Evil Mad Scientist page