I think almost every AI-guy have tried making a boids simulation. They are such a good way to show emergent behavior from very simple rules.

I'm a TA for an AI-course at my uni, and this semester my students had to program a boids simulation for the first project. In addition to what's shown here, the boids also had to avoid obstacles and flee from predators. I think the students liked it, it's very rewarding to code and actually see the result.

The students also had to implement sliders, for how much cohesion, separation and alignment is weighted. It's pretty fun to change them and watch the behavior of the boids change.