I go by the principle that a pizza is just a toastie without a lid so anything that makes a good pizza makes a good toastie… so:
mozzerella, basil (or green pesto) and tomato
ham, cheese and pineapple (I know I will get roasted for that one)
gorgonzola, pear and mushroom
spinach, mozzarella, tomato and egg (actually I just love an egg in a toastie on its own!)
4 cheese, tomatoes
bbq beef, green peppers, mozzarella, bbq sauce, tomato
black olives, mushroom, mozzarella and tomato
artichoke, mushrooms, onions and black olives
As the rule I add spring onions to toasties over normal onions as then you don’t get that raw onion feel
I also love leftover bolognaise or chilli with cheese in a toastie