Preheat grill to 350° to 400° (medium-high) heat. Remove husks from ears of corn. Coat corn lightly with vegetable cooking spray. Sprinkle with desired amount of salt and pepper. Grill, covered with grill lid, 15 minutes or until golden brown, turning occasionally; remove from grill. Stir together mayonnaise and sour cream. Spread corn with mayonnaise mixture; sprinkle with Parmesan cheese and chili powder. Cut limes into wedges, and squeeze over corn.