Internet Controllable Thermostat

Proliphix produces an internet connected programmable thermostat that uses your LAN as its power supply with the aid of an (additional) ethernet power adapter. The thermostat's configuration/monitoring webpage is accessible from within your home network as well as from the internet. The company also offers wall mountable and paintable sensors to increase whole-house temperature accuracy. From the site:

Proliphix offers indoor temperature sensors, which can be mounted away from the thermostat so that temperature inside a home or small business can be averaged across multiple rooms to avoid hot or cold spots and wasted energy. With an optional Proliphix outdoor temperature sensor connected to a networked thermostat, the heating/cooling system can be controlled more precisely to efficiently and more comfortably overcome the indoor to outdoor temperature difference. The web browser configuration tool is simple to use and allows users to easily configure heating or cooling programs to maximize comfort and minimize energy use.

Smarthome sells the Proliphix NT20e, which is the same unit but with 2 additional remote temperature sensors, for use in monitoring different zones within your home or even the outdoor temperature.