I've always like Jimmy Johns vegetarian sandwich. Especially when I order it on their thick cut multi grain bread. I'm trying to remember it off the top of my head, but it's got guacamole, provolone cheese, mayo, lettuce, tomato and sliced cucumber - and you can optionally add roasted hot peppers, which I highly reccomend. It used to have bean sprouts as well, but they took those off the menu a couple of years ago when there was a contamination issue at their stores. They put a lot of cheese on the sandwich too, like several slices, so it's not exactly health food, lol.
Another favorite sandwich I make is with those jarred Italian hot peppers - not the neon yellow hot banana pepper rings, these are hungarian hot peppers packed in oil with some garlic and oregano. You can usually find them at the olive bars in most grocery stores that have them, or in jars in the Italian specialty food section of the store. Some hard salami, smoked provolone and those peppers go great together. But just the cheese and peppers alone are fantastic too. The peppers also go great with turkey lunch meat.
I've also made sandwiches with hummus, sliced cucumber, lettuce, tomato and red onion - then also put an olive tapenade spread on the other side of the bread.
Grilled chicken parmesan sandwiches are also great. Just be sure to use a sturdy crusty loaf of bread, like a french bread. Simply grill up some chicken breasts and cut them into strips. Smear some marinara sauce on both sides of the bread, and add your chicken and slices of mozarella cheese. Nuke it in the microwave a bit to get everything heated through and melty.