Muscadine. Grew up only getting this when visiting family in Tennessee. I still eat my fill every time we visit.
I honestly don't know if it's produced, or rather available commercially. I'm not a huge jelly or jam person. To be honest I use it to baste ribs more than anything. I'm sure with as many local shops and farmer markets as there are popping up, it's likely you could find it.
We have homemade orange, tangerine, and wild muscadine jam/jelly/scuppernong, but lemons my personal favorite
Sweet Tea jelly made with "spicy" tea packets I don't recall the brand of off the top of my head. Has cinnamon in it, and other good things.
Freaking love apple butter. An added bonus is that no one else in my house does, so I never have to hide it!
Real orange marmalade (I had my first taste of the real stuff in Morocco) is impossible to beat. Everything else is a distant second, although I like blackberry, raspberry, mulberry, etc.