My skillets, pots, and pans are notorious for getting food stuck on them, and many times I've burnt food in them (I'm newly domesticated...). One of the ways I clean up is by putting vinegar, warm water, and a small squirt of dish soap in, letting it sit for a few minutes, and then boiling it for a few minutes while stirring.

Also, to clean my sponges, I soak them in water with vinegar and lemon juice, then microwave them for about 1 1/2-2 min (KEEP WET! or they will ignite.).