Weber makes a grill spray that works well, but it is kind of hard to find. I use a General Mills commercial pan release product that works very well and doesn't flare at high temps. On my grills with metal grates, this makes for some good seasoning. On my grill with porcelain grates it has to be re-sprayed (like the Turtle, I spray it on the meat) when turning during the cook. Also, just a little spritz will keep the GrillGrates working beautifully.
Hub