There's a mustard that's made in Rock Island, Illinois called Boetje's.
Maybe it's just my roots talking but this is still the single best spicy mustard I've ever had. It's unapologetically hot and tangy, and I've never found anything better for bratwurst or sandwiches. And no one from outside the Midwest has ever heard of it. I was still able to get it when I moved to Kansas City, but then when I uprooted to Connecticut I finally left Boetje's range.
What are some of your favorite lesser-known regional condiments? Not famous stuff like Duke's mayo.