Here is a really neat new gadget from SparkFun:
The Breakout Board for SC16IS750 I2C/SPI-to-UART IC, which allows adding another UART and communicating with it via I2C or SPI. I really want to get a couple of these to see if I can successfully add more UARTs to a microcontroller. I can see where adding one or more of these to a microcontroller board would be very beneficial. I want to use these with my BeagleBoard, Arduino, and Sanguino.
I bet these would be useful on a BotBoard II type board also. 
8-Dale