The Arduino is truly a fabulous piece of kit if you are new to the world of micro controllers. There are hundreds of examples of hardware projects on the web along with the source code that drives them. My latest project involved the use of an ethernet shield which allows the Arduino communicate with your LAN and therefore the internet. I can now control my flashing LED‘s remotely (actually my test involved being over 15 miles away) using a web browser. Still early days I know but a quick search on Google will give you some ideas of the possibilities. Next step I think is to add a sensor and read some values. A simple circuit should be able to read temperature or a PIR detector from an alarm system would allow me to remotely check if somebody is in a room.