This might be of interest. I was looking at this when we were going to rebuild our house and try and implement a bunch of "green house" improvements, which mean lots of things to lots of people, so that's a long story.
Any way, this is an interesting monitoring system, less so control, makes a lot of use of i2c. http://www.welserver.com/
Mr house is an interesting and long running software control project. It started as x10, but I think has other com methods now. http://misterhouse.sourceforge.net/
I did this for a living for awhile, mostly in a museum, but I can tell you what was cool, oh ten years or so ago.