A complex LED flasher? Maybe one that instead of flashing, smoothly fades the LEDs in or out?

Want to run that lawnmower more efficiently and cleanly? Be the first on your block with a mower that has an onboard engine management controller.

Of course: robots, robots, robots.

A Newton's laws demonstrator that times how long it takes from when you release it to when it hits the floor and uses that to calculate the initial height. Bonus points if it displays G force when it hits the ground so you can experiment with different types of padding.

A temperature controller for your overclocked game machine?

And that's just simple hobby stuff without even getting into real industrial uses!

I love being a hardware hacker!