PLC-BUS works well using Dan's Ruby based integration.
in the wiki and http://wiki.linuxmce.org/index.php/Setting_Up_PLC-BUS_Template
to set up your devices.
I have a USB based interface and a dual crystal light switch. These work as expected and I have no real complaints with them. Reliability is excellent and speed is good.
There is a X-10 bridge available as well but I have not used this so can't comment.
I am using these in Australia and these seemed to be the only real option available except for X-10. I plan to get some more in the near future.