[Varmint]

To me, macaroni and cheese is one of the finest dishes one can make on a cold day (yes, I'm dreaming of fall already). Plus, the kids love it. I've made mac & cheese with lots of different cheeses, but I'd like to hear from you what cheeses you would suggest for this dish that might be a bit off of the mainstream.

[master cheesemonger/grocer]

Read this and insert "macaroni and cheese" everytime I have typed "grilled cheese sandwich".
I am particularly partial to the grilled cheese sandwich my wife and I raised our boy Max on: Open-faced slice of bread spread with sweet butter or olive oil liberally sprinkled with grated Parmigiano Reggiano, placed horizontally in the toaster oven until the Parm bubbles, cut into triangles.
I am equally smitten by the conventional closed-face grilled cheese sandwich using sourdough or rye or whole-grain slices and shredded mountain cheeses such as the following spectaculars: Beaufort from Savoie, Fontina d'Aosta from Aosta, Comte from Franche-Comte, raclette cheese from either of these two regions, any Basque sheep's milk cheese (Erhaki, Matocq, Ossau-Iraty, Etorki, Prince de Claverolles), Roncal from Navarra. Certainly Swiss Gruyere or Emmental or Appenzeller figure, though they're way down my preference list. Also Asiago from the Veneto, Majorero (unlike the rest of these, Majorero from Fuenteventura in the Canaries is NOT a raw milk cow's milk cheese, but is a raw milk goat's milk cheese), Sao Jorge (St. George, a sharp cow's cheese from the Portuguese Azores). Both sides of the bread are spread with sweet butter, occasionally mayo (I prefer butter), occasionally a slice of tomato; the cheese is always shredded, not place aboard in slices, I always add a liberal amount of freshly ground pepper, occasionally I'll dribble some hot sauce atop before closing the sandwich, lifting it via a spatula and placing it into a buttered or olive oiled hot skillet, turning it once and removing it when the bread has nice color and the cheese is beginning to melt onto the hot skillet. Rarebits call for Mrs. Appleby's Cheshire or Mrs. Kirkham's Lancashire or the Keen's or Montgomery's Somerset Cheddar, but they're not really a good choice in this regard. Plus, they're melted and poured over toasted bread as for a proper Piemontese fonduta, so they don't really qualify as grilled cheese sandwiches. I like the smell and taste of melted mountain cheeses much more than melted English cheeses which are a completely different type (recipe) of cheese (cheesemaking).
So, you asked me about mac and cheese but my brain read grilled cheese. No matter. These are the cheeses that will give your mac and cheese jones a whole new drug.