Here's a bus ad that's better than most.

(click image, via)
For extra strength Bayer Aspirin®, currently on the backs of several Toronto city buses, according to the agency press note. Bus driver hits the brakes, the lights simulate the pounding pain. It's a bit creepy, but it's simple and it works. Smart media buy. Previous cool bus ads: Crayfish on a bus! • Snake on a bus!