I second the reuben, and although I’ll generally get it with corned beef, I’ll have a pastrami one every now and then.
I also love grilled cheese sandwiches with tomato soup. Juvenile, yes, but a great comfort food.
I’m surprised nobody mentioned a hamburger. And I’m not talking about your typical fast-food burger. 1/3 lb, medium rare, grilled bun, with sauteed mushrooms, bacon, cheddar cheese, and A-1. Or (for the adventurous only), the same patty, but instead of the previous trimmings, just wrap the burger in a plain omelet, salt the crap out of it, and serve it on a butter-toasted bun.
I’m not sure if a hot dog counts as a sandwich, but chili dogs with Cincinnati-style chili can’t be beat. Sprinkle on a bit of diced onions and some finely shredded cheddar cheese.
I don’t generally like condiments (I can deal with A-1, horseradish sauce, and spicy brown mustard, but that’s it), so my favorite way to add both moisture and texture to just about any sandwich is cole slaw. Sounds weird, but it’s good. Try it.
Wow, I’m hungry for the first time in days.