My new project, is a simple led-strip which shows CPU load. 9 led's are used for this, could have used more but my tiny breadboard couldn't hold more. Anyhow, it uses serial communication to receive how much the totalcpu usage is. For this I use a C# program I wrote, it just sends a values from 0-100. And the Arduino reacts and lights up leds accordingly to how much load your CPU got.