I love leftovers. I come from a large family and now that I have my own place with only one housemate, I struggle to cook small portions - great for lunches the next day or to freeze and reheat when I'm busy or don't want to cook.
The types of foods that are my staples are generally pretty good reheated: Chilli, curries, soups, stirfry noodles, pasta bakes, etc. Like Steve said, some of those things are even better after a few days sitting there while the flavours get to know each other. I make a pork chilli verde which is better on the second day, more depth of flavour. It makes a major difference whether you reheat in a microwave versus stove top/oven though
I don't like leftovers with chicken. Reheated chicken has a weird taste. It's the same reason I can't stand chicken on pizza, it's cooked first then reheats when the pizza cooks. Beurk.
Cold pizza however, is a god among leftovers.