Oliver over at ELMICRO told me about a great new board they've put out for mbed. Meet the mbed TestBed!
Looks like a great platform for easy access to all the signals. Here are all the details from ELMICRO:
"TestBed is a versatile carrier board for the mbed microcontroller module. The TestBed provides interfaces for RS485, RS232-TTL, CAN and Ethernet as well as an XBee socket which grants access to the ever-growing family of wireless communication modules being available in the popular XBee form factor. It also provides the necessary power supply circuitry and a 100mil-spaced prototyping area, and even a socket for Arduino shields!"
You can also get it as a complete starter kit with mbed and TestBed, a white-on-blue 20x4 alphanumeric LC display, cables, connectors and mounting material plus a wall plug power supply unit. You can find out all the details at: