Two of my favorites right now:
1) Pesto and Tomato Panini: Ciabatta bread, spread homemade pesto on each side, add some Tomato Garlic oil (I use Cheeky Monkey out of Syracuse), thinly sliced Roma Tomatoes, and real Mozzarella cheese and then press it in a panini press.
2) A true Cuban - Cuban Bread, Mustard, Pickles, Swiss Cheese, Ham, Roasted Pork, and Butter. I've seen some places also add Salami, but I prefer it without.
I'm not a huge Rueben fan, but the one I had at Zingerman's deli in Ann Arbor was incredible. I've tried a few times to replicate it but I can't quite get there. It must be either their own dressing or the way they do the Kraut, but who knows.
When I was younger, my mother and grandmother used to make homemade Porchetta sandwiches. Those were incredible. Unfortunately, I don't have her recipe, which was passed down from her mother. I've tried a few recipes online, but it's not the same. Plus, my wife doesn't eat beef or pork so it would be too much for 1 person.