Besides the ideas in this video, here are some others that students have come up with:
A car with a horn you can turn on or off'
The night sky, using LEDs to represent stars;
Fireworks;
Fireflies;
A thunderstorm, using a buzzer to represent thunder and yellow LEDs for lightning;
A volcano, using a buzzer for the roar, and a red LED for the glowing lava;
An airplaine or helicopter, with a motor turning the propeller;
An intersection, using red, yellow and green LEDs for the traffic light and a buzzer for street noise;
A picnic scene, using a buzzer to make the sound of a bee.