I am working on a breath-to-breath phy2phy project. I already had one Arduino NG around, so I purchased an Adafruit Ethernet Shield, and also a Modern Device Bare-Bones Board Arduino clone with a USB-to-TTL serial cable.
The BBB board had a couple of holes that were still filled with solder, so I had to solder wick them and then heat up a little piece of lead snipped from a resistor and used the soldering iron to heat up the lead and push through the solder-filled holes to open them up.
Just to be clear, standard Arduino shields do not fit on the Bare-Bones Board (so I probably should have purchased a Really Bare-Bones Board), but you can always hook it up with wires.
I am developing for the Arduino and BBB on a MacBook using the USB to TTL serial cable fro FDTI. Make sure you follow the OS X instructions on how to install the FDTI drivers. These will allow you to use either a USB cable to a Arduino or the FDTI USB to TTL cable for the BBB/RBBB. Also make sure you choose the correct ATMEGA chip from the Arduino software menu. And since there isn't much indication that the BBB works (unlike the flashing LEDs on the Arduino), so try a serial example on the BBB to convince yourself that you are uploading and running a program.
Here is the Ethernet shield on an Arduino NG:
I am awaiting two Xport directs in the post, then I can really get to business.