I like to put sauteed onions, jalapenos, bacon, and mushrooms with ketchup and mustard. Also maybe cheese.

I also like chillidogs with cheese and mustard. (with real hotdog chilli, not the crap Megan mentioned.)

I also like them with chipolte, or crushed up bbq potato chips.

Boston style with a poppy seed bun, tomato, onion, and those little green peppers is good.

Knockwurst are superior to bratwurst.