In my experience, the perfect cat toy is a laser pointer. Flick it on and your cat will chase the little red dot until you get tired. Across hallways, up walls, and onto people - much fun is created by proper laser pointer use. I'd be careful not to shine it in the cat's eyes though.

One more thing to watch out for - the advanced technical concept of "amusing cats with laser pointers" is patented. (This is not a joke.) Oooh, I'm breaking the law, breaking the law! And amusing/excercising my cats at the same time. Beat that! (I fear the author of Mom, I Gave the Cat Some Acid very well might have.)