If you painted your pumpkins this year (or decorated them in some other way that didn't break the rind), you can likely reuse them in a myriad of ways in the kitchen. But even a carved pumpkin that's rotting fast can be put to use in a way that will eventually return to your kitchen:
Compost it! Use it as compost to enrich the soil in a garden or planter. This can be done in a couple of ways: For those with a compost bin or pile, smash up ol' Jack and add him in - it will easily break down and contribute to a nutrient-filled compost for enriching your soil. Even without a compost system in place, you can simply bury a used jack-o-lantern and it will break down in the soil. Adding it to the garden will give life to wonderful new fruits and veggies to be enjoyed next year!