Pi Supply's Pi-Crust: The expansion board called 'Pi Crust' makes it easy to connect numerous devices to the Pi. The compact board is mounted on the Pi (see picture) and increases the overall height by less than 2 mm. In addition to numerous ground and 5 V pins, GPIO, I2C, SPI and UART are also brought out. The Pi Crust can be ordered for 13 pounds at www.pi-supply.com.