Our favorite sauce for cheeseburgers is fry sauce. This is basically just a mixture of ketchup and mayo, though we add a splash of vinegar. u003cbr/u003eA spicy barbecue sauce and a few slices of avocado make a great burger.u003cbr/u003eSome of my friends add butter to the burger and let it melt before adding their other toppings to the burger. Delicious!u003cbr/u003eOnce, my husband even ordered a peanut butter burger from a local restaurant. We haven't ordered it again, but it was fun to try!