The SmartMatrix board is a 32×32 RGB pixel RGB display (other sizes are available), and it makes an eye-catching display. There is an existing code library to run it from a Teensy 3.1 with a SmartMatrix Shield. The hardware setup and code library are documented at the pixelmatrix website. The library has all kinds of cool looking built-in effects, like text scrolling and geometric shapes.
The easiest way to program the Teensy is to add the TeensyDuino extension to the Arduino IDE. Once the extension is setup, the code can be written in the IDE, and it is loaded onto the Teensy board just like an Arduino. The only noticeable difference is that the code does not automatically load if the Teensy is running a program. In that case, you have to press the Teensy’s “reset” button to complete the loading of new code.