I just moved to Durham from NYC, and recently had the best sandwich I've ever eaten (outside of NY, of course).
It was the flank steak sandwich at George's Garage, on a sliced open flatbread with mesclun greens, herb mayo, tomato, and drizzled with their balsamic vinaigrette. Not the cheapest sandwich in the triangle, I'm sure, but at &6.95 it still is reasonable.
If you've had better, I'd be shocked, but would like to know where!!