The best comic book character ever was Becassine.

I was under the impression that kryptonite was really just a green-tinted plastic shell with a light-bulb inside it. At least, I'm pretty sure that's what it was in the first Superman movie. . . .

Hm. They identified it as "kryptonite" based on last year's Superman Returns film. However, comics continuity often differs from film continuity, and I don't recall seeing any other "flavor" of kryptonite in the films.