What are some good charlieplexing LED matrix boards for the Arduino that use very few pins? About 3 digital pins would be great.
Also, I am looking for a good interface to control the LED matrix.
Using 3 I/O, you can only charlieplex 6 LEDs. The board would require an I/O expander, which would take up space limiting the area you could place LEDs.
However, a very functional, full color matrix LED board is available at a reasonable price from Adafruit: the Adafruit NeoPixel Shield. It's listed for under $30 right now, and requires only one digital pin. If you plan on using all the LEDs at full brightness you'll need a fairly powerful power supply - 5V at 3A or more should do it.
Further, the libraries are already made and included, so the interface is easy.