Learn to monitor and control your home & environment with self contained, inter-communicating microprocessors. Applications include ham radio, robotics, weather stations, model railroading, toys and more. - KK4HFJ
Want to get started playing with Arduino's, but don't have the hardware? Download a free (or nearly free) simulator from http://www.arduino.com.au/Simulator-for-Arduino.html. This is a good way to get a feel for the platform, it's abilities, and the code, before making investments in hardware and accessories.