On Saturday I picked up an Evil Mad Scientists Arduino clone, The Diavolino, from MadLab‘s little shop “Invent-ory” to use with my RS485 stuff. the Diavolino requires assembly yourself (official instructions).
The FTDI I bought was this one: RHX PL2303 USB To RS232 They are about £2.29 per. however where Windows 7 will grab the drivers from Windows Updates, there is a little bit more work to get it to be happy on a mac:
You can now download the drivers from http://plugable.com/drivers/prolific/ or PL2303 MacOSX-10.6 up v1.5.1
Install the drivers by following the instructions in the zip, reboot the computer, and plug in the FTDI board (copy wiring from above). load the Arduino IDE and select the board and serial