This sketch creates a HTTP server and waits for incoming HTTP requests in the form of
# is the a number from 1 to 3.
You need an etherned shield like this one from watterot for this. Works fine with an Arduino Uno.
It also provides a simple HTML website for sending the HTTP requests. If you prefer to use your mobile phone/tablet have a look at arduinoRCLightSwitchApp.
Change MAC/IP-address and the amount of light switches you want.