I'd just use simple RS-485 and software serial with a simple protocol.
Obviously there's going to be more than one way to accomplish this. I'm just curious how any of you would do it.
What converter(s) do you use for rs485?
Ccc56: As CD says 485 is only a phyiscal layer you still need to write a protocol and AFAIK there is no simple standards. From what I can see you have a very simple application with no control, just monitoring.