X10 Lighting and appliance modules are cheap on Ebay, I wanted to control them with my HMI (ScadaBR) so I put a X10 and Modbus library together in an Arduino to turn on and off the modules.
The Arduino can control the X10 Firecracker CM17A using a library found on the Arduino website. http://playground.arduino.cc/X10/CM17A
The library comes with a cool demo sketch that will loop through and turn on and off an X10 module.
I merged the CM17A code with my favorite Arduino modbus library so that I could simply write to coils in the Arduino to command X10 modules. https://code.google.com/p/arduino-modbus-slave/
It was then a snap to set up ScadaBR to command the modules on and off with any device with a web browser such as my windows phone.