Well I know my husband adds onions, bacon and Worcestershire sauce. Me - well all I add are a few chopped mushrooms. :-D
I like to mix the cheese. Sometimes I add cream cheese or extra sharp along with good old cheddar. Good old home grown 'maters are good too Deanna :-D
I don't use anything but very good fresh cheese. I guess that is easier to do when you live in Wisconsin.
Like Jungseed, I'm pretty spoiled living in here and don't add anything to mine...but some of your ideas sound pretty good. I'd be tempted to try something healthy like fresh spinach (I put spinach in almost everything).
When i lived in America, i used mayo and pickles on my grilled cheese. Here in Norway, one slice of bread is a sandwich. so i put the cheese, add some dill, basil, or any herb really, some red sweet pepper rings and leek, put in the oven to toast, then add homemade salsa or sour cream. and enjoy,, open faced sandwiches are the normal here.
Goodness, Biita, that sounds amazing! I like to use a good sourdough, a very sharp cheddar, and thin slices of a homegrown tomato. ChefsRUs, if you are putting together a cookbook, you certainly scored big in this category, lol!
Followup: Just happened to have some dill onhand so I made a Biita grilled cheese, added some green onion- I Highly recommend it!!
I like to vary the cheese I use, provolone, cheddar, american and a mixture...pepper jack is always nice. Crispy bacon, ham and tomatoes are very yummy.
When I was working in the states I discovered Velveeta cheese. If you use this your tosted cheese sandwiches will be like bo one elses. I Liked them with crispy bacon strips and avacado slices.