Heat grill over medium heat and spray rack with non-stick cooking spray. Grill corn, turning frequently (so they don't burn), until the corn is slightly browned and heated through. (about 8-10 minutes) Meanwhile combine the mayo and sour cream in a small bowl and whisk until smooth. In another small bowl combine the chili powder, salt and pepper. Slather the hot grilled corn with mayo/sour cream mixture (I use a pastry brush to brush it on), then sprinkle with the chili powder mixture. Coat in the parmesan cheese, and sprinkle with the chopped cilantro. Serve with a lime wedge (use the lime to squirt lime juice all over the cobs). Enjoy!