These are the 2 basic ingredients. Be creative with toppings. Butter the outsides of the tortillas, fill with cheese and toppings. Toast both sides on medium until cheese melts. Cut into wedges (easiest with pizza cutter).
Pizza quesadillas: Mozzarella cheese, pizza sauce, pepperoni, green peppers, & onions
BBQ quesadillas: Mozzarella cheese, bbq sauce, shredded chicken
Mexican quesadillas: cheddar cheese, refried beans, salsa, maybe shredded roast beef or leftover taco meat
Green chili quesadillas: mixed cheese, canned green chilis, and chicken
Quiche quesadillas: scrambled eggs, swiss cheese, bacon pieces, and sauteed onions