There's a local pub that used to serve one of the best grilled cheese I've ever had. For the life of me, I can't recall what cheese they used. But it was on Texas toast, and in addition to the cheese (which was fantastic), it had thick cut sriracha candied bacon and grilled hatch chile pepper, caramelized onions, and thin slice of tomato.
I'm all in favor of going fancy with grilled cheese. But I'm also fine with the basic as well.
EDIT: Just found an old menu online, and it said they used brioche instead of Texas toast, so I may have been wrong about the bread. But I do remember it was sliced pretty thick, but still toasted well. They also said they used mozarella and cheddar, and while I do recall it being a mixture of cheeses, I seem to recall there being more of a tangy cheese as well.