Scrub your cast iron with coarse salt and a soft sponge. The salt is a natural abrasive and will absorb oil and lift away bits of food while preserving the pan's seasoning. Rinse away salt and wipe dry.
My bathtub has never been whiter!! Works great on glass shower doors too- no more soap residue! Martha Stewart's Tub Scrub--works better than any other cleaning product to get off hard water and soap residue. 1 cup baking soda, 1 teaspoon dish soap, enough water to make a paste.