rain8net with my own software running on a unix system. I'm really really happy with it! Them actually - I have three of them all daisy chained off one serial port. No pretty graphics displays, but it does exactly what I wanted - nothing more, nothing less.
Two are used for irrigigation (one front yard, one back), and one is used for water control on my outside fish ponds. Very convenient! They use cat5 to extend zones. I think it uses RS485 between the modules over cat5 cable. It transports power over the cable too, so you probably don't want too big a run.
I also have an ontrak.net ADR2205 for other things around the house. I had that leftover from a halloween project and it picked up other uses over time.