when jersey or georgia peaches are in season, i love to grill them with some brown sugar or honey.
freestones are the best since the pit comes out easily, so you can slice them in half, pull out he pit, double skewer them a couple at a time all facing the same way. i like to spray the open side with a little cooking spray, grill them with that side down jut to get marks, then turn them over. sprinkle brown sugar or honey on the open-grill marked side, and close the lid to let them warm thru and the sugars melt, and they get a little smokey.
pineapple is my second favourite fruit to grill, interleaved with chunks of teryaki marinated fish and sweet onions.
pear halves are also good to grill, and when almost done, sprinkle the tops with a little crumbled gorgonzola and chopped walnuts, drizzle with evoo, again - close the grill and let the cheese melt and smoke.
i'll have to try apples this year since my grill is right under my apple tree. in august and september you have to watch out for falling apples when using the grill. i've gotten plunked on my melon so many times that even worn a hard hat and a petzl head lamp at night when trying to grill.