I just got my Ardunio for Father's Day so the only sensor I have on hand is a LDR. I wanted to do something with the LDR other then what I had done with my getting started book.
The idea is simple, the LDR reads the ambient light, and lights up one of the three LEDs depending on how bright/dim it is. After making it, I added a sensor output just to help me troubleshoot a small problem I was having with the yellow and orange LED flickering. (The Fritzing file shows a white LED only because there is no orange)
I have almost zero background in electronics, and very little in programming, so this was/is very exciting for me! Link to a small video I made of it working. I am tilting it away from the light source, not using a tilt sensor in case you were wondering.