OK, I'll start. The smell of caramel corn takes me back to being a little child and going to our neighborhood Fedco. Even now, though that store has since become a Target, I can still smell that popcorn even though it's been gone for years.
Also, the smell of tomato soup brings me right back 2nd grade in my elementary school's cafeteria. It's not a good memory, but I love homemade tomato soup :)