Pinwheels with lights and a microcontroller. One model would just have lights that would randomly turn on when the pinwheel turned. Another would be a POV that would use a gyro to measure the spinning speed and then light up accordingly.
There are a couple technical challenges: 1. Is the material too heavy to spin? 2. How do you power the circuit? etc. I know my kids would love a product like this I would love a product like this.