This instructable shows you how to build a Web-enabled tri-color LED based on an Arduino and the WIZnet Ethernet shield, controllable from any Web browser .
Because the LED is exposed through a simple RESTful web service running on the Arduino color changes can also be triggered by Pachube or other platforms offering Web hooks. Welcome to theWeb of Things ! The LED can of course be replaced by a motor or a high voltage switching relay to enable more interesting browser controlled applications, e.g. for home automation.
Publishing your Arduino through the Yaler relay server makes the Arduino accessible from everywhere even if it is hidden behind a firewall or a NAT and does not have a public IP address. A single Yaler relay server instance can host many Arduinos (and any other device with a TCP Socket library, e.g. a Sheevaplug or an Android phone) and is available at https://yaler.net/ (Disclosure: I'm a founder of Yaler)
(Note: All images show the Adafruit LED with the corresponding resistors and wire color)