Grilled Cheese Sandwich Recipes

Well, I was thinking about a recipe for a crazy hot day like today, and what came to mind but the trusty old grilled cheese sandwich. The link will take you to a site featuring the search for the Greatest Grilled Cheese Sandwich in America. I'm going to presume that the authors imagine this applies to Canada as well.

I make mine with old white cheddar, lots of dried chili flakes, and butter - never margarine on a grilled cheese, please. I prefer them on anything but processed to death white bread, although I know that is a sacrelige to the true grilled cheese junky. There is a faction out there that insists on mustard on a grilled cheese? Is that allowed?

What magic ingredients do you add?