PoEthernet Shield from Sparkfun

Ethernet connectivity is a great way to get your Arduino talking to other systems all over the world (or at least the network). But sometimes running an Ethernet cable is hard enough, why should you have to run a power cable too? That’s where PoE comes into play: Power over Ethernet.
The PoEthernet Shield not only give your Arduino access to the Internet via the Ethernet Library but it also allows your project to power itself from the Ethernet line (provided you’ve injected power to it somewhere down the line).
This is a board based on the Wiznet W5100 ethernet chip.