Right now, we're using Meijer Organics ketchup. It does have vinegar, and I have no idea if the vinegar they're using is corn derived as I haven't called on it yet. I haven't noticed any reactions, but then maybe I haven't been observant enough- you never know.
I did call about the regular Meijer ketchup, labelled "no high fructose corn syrup". It does have "natural flavors" and those ARE corn derived according to Mr. Storm. He said that this is so it can be gluten free- which is fantastic, if you're gluten free.
I've been thinking about making my own, but haven't gotten around to it yet. Anyone have a recipe they'd like to share?