For an interesting project with younger people or just for fun, you can build a device that tracks the sunlight outdoors or any other strong source of light. By using an Arduino that measures the levels from five light-dependent resistors, it can determine from which direction the light is the strongest. It then controls two continuous-rotation servos to move the device in the direction towards the light source. Although the creators used a ... lot of cardboard, you can recreate it from anything spare. For example:
To get started with your own sun tracker, check the instructions out here. And we're on twitter and Google+, so follow us for news and product updates as well.