The folks over at Serious Eats offer up this snazzy use for leftover Peeps: S'meeps!
You don't necessarily need a recipe but they offer one up anyway. In an egg, er, nutshell: Lay a square of chocolate on a graham cracker square. Top with Peep and bake. Squish.
Considering the rainbow of colors the marshmallow-y treats come in, it'll be as if the Easter Bunny blew up in your kitchen. Imagine that. Or don't.