Go grab the latest issue of Make Magazine! In addition to it having a wonderful run down of many of the different types of Arduino or Arduino-like boards out there, it also includes a project Mike & Tod created: CloudFridge. CloudFridge makes your fridge door Internet-connected, creating a real-time graph of when and how long the door is open. Applications of this data could range from a simple fridge energy monitor to diet planning. But mostly it's a demonstration of just how quickly one can go from idea to working implementation with tools such as Arduino, BlinkM, and Xively: we went from idea to working implementation in an afternoon.
We originally created this article over a year ago and its showing its age a bit (today the Arduino Yun would be a great alternative to what we used), but the techniques are still very valid. Thanks to the Make magazine staff for helping update the article in the light of the Pachube->Xively transition. And check out this awesome cute title graphic they made for the article.