The Arduino platform lends itself well to getting into the world of home automation (check our SuperHouse.tv) and many enthusiasts have created their own systems. However one home system by Arduino forum member OhmMega is of interest due to the controls and possibilities.
This system can act as an intelligent thermostat control, taking temperature and himidity reading from various sensors - and controls a furnace and HVAC to keep the users' climate in check. Furthermore lighting and other devices can be controlled without much effort. The system has a web-based interface and also a mobile page for use with a smartphone.
An external server is used, based on php/MySQL with a client-server http communication protocol, and takes care of communication between the end user and Arduino-based hardware which acts as a clint with its own login to the server. All this adds up to a great system that's ripe for modification.
If you're working with Arduino, Ethernet and home automation - check out the Freetronics EtherMega:
Quite simply the EtherMega is the fully-loaded Arduino-compatible board on the market today. Apart from being completely Arduino Mega2560-compatible, it includes full Ethernet interface, a microSD card socket, full USB interface, optional Power-over-Ethernet support and still has a circuit prototyping area with extra I2C interface pins. So if your project is breaking the limits, upgrade to the EtherMega today.