Salt, Pepper
Salt, Pepper, Garlic (granulated)
Salt, Pepper, Chili oil (rayu)
Pre-mixed toppings, in all their varieties.
Chinese 7-pepper
Thick slice of fresh Pineapple (put on while grilling - after flipping it once)
Multiple cheeses
As a unique burger, I love a good layer of melted mozzarella cheese on a thick beef paddy, shredded lettuce, mustard and Italian dressing...on a fresh sourdough bun.