Learn to monitor and control your home & environment with self contained, inter-communicating microprocessors. Arduino / Raspberry Pi Applications include ham radio, robotics, weather stations, model railroading, toys and more. - KK4HFJ
I highly recommend you download Sparkfun's Inventors Guide. It will give you a lot of valuable information on how to use the Arduino, trigger some neat ideas of your own, and Sparkfun is a valuable resource for components and sample code.