Hi, all. This is my first post here. I have to second the recommendation of Bauer's mustard made earlier. This is the best mustard in the world, in my opinion, although I admit to a slight bias because their factory is just up the street from my childhood home
They offer two varieties of brown mustard, with or without horseradish, and they're both superb.
Pulaski (mentioned in the same post) is also very worthy, almost as good as Bauer's. Kosciusko is like Pulaski, but a bit less spicy. (Both are named after Polish Generals, by the way).
Also, I used to love a super-coarse (as in, the mustard seeds were nearly whole!) brown mustard made by Plochman's. It came in a rather big jar. Although Plochman's is still around, I don't believe that particular variety is offered anymore; at least I haven't seen it in twenty years.