I made a Fatty Piston and have used the heck out of it. I'm not sure how many things I've stuffed in a fatty, but it's several dozen by now.
My absolute favorite was a beef tamale fatty, with lean chorizo in place of sausage.
My other favorites have been, in no particular order:
Philly Cheesesteak Fatty
Denver Omelet Fatty
Corned Beef Hash and Eggs Fatty
Biscuits and Gravy Fatty (no milk in the gravy--powder mix and water)
Supreme Pizza Fatty
Blueberry Pancake Fatty (best breakfast ever?)
Pecan Pie Fatty (best dessert ever?)
Leftover Turkey and Cranberry Sauce Fatty
Leftover Stuffing Fatty
Potroast and Taters Fatty
You also can't go wrong with a plain fatty with good sausage and a good rub/sauce.