My favorite so far has been dried cranberries and then about an hour before the oatmeal was to finish, I diced up some fresh apple and stirred it into the mix. The apples got warm but not mushy and it was SO good!
I also love to add walnuts, after the oatmeal's cooked.
This recipe makes enough for my in-laws, my kids, and me for one morning (three adults and three kids 6 and under). We only had leftovers once, when I increased the recipe by 1.5, and I refrigerated them and the kids ate them the next day, warmed in the microwave.