A few that I've discovered myself are also quite tasty. Let me share them with you:
The ABC is an apple, bacon, and cheddar grilled cheese. The combination of flavors is hard to pass up. You just fry up a few slices of bacon, slice up your apple (I prefer Granny Smith's) into thin slices (look at the picture, that's a good size) and put a slice of cheddar on either side of the bread, with the apple and bacon in the center. It's simply wonderful.
The Ultimate Grilled Cheese.
The Ultimate Grilled Cheese is all about excess, so be warned if you don't like greasy things, this isn't for you. What you do is combine 1/4th cup of mayo and 2 tablespoon's of cream cheese. You whip this up until it's blended together. Then you add in 1 cup of cheddar, 1 cup of mozzarella and a pinch of garlic powder. mix together, then spread on your sandwich. Bear in mind, this is enough mix for two sandwiches, usually. What you get is a creamy, gooey mess of delicious. I've also experimented with using a cup of havarti or a cup of colby jack in for cheddar, and it still turns out amazing. This is also 1/5th of a recipe I took from the internet. The original version was a huge batch that would be used to make little 2x2 sandwich squares as hors d'oeuvres. I've not found the occasion to make that yet, but I want to.
Enjoy your fancy grilled cheese!