One I like is mushrooms, onions, peppers (I use jalapenos), bacon, and whatever flavor of cheese you want to throw in.
I've never made a bad one, but some I like better than others. I've used 1/2 sausage & 1/2 hamburger. But that may not really be a fattie by definition, maybe more like meatloaf.
Pizza fatties are good. Just use a little pizza sauce, and your favorite pizza toppings. I've never used italian sausage for a pizza fatty, but it's on my to-do list.