McDonald's: Big Mac or Quarter Pounder, although from time to time I will get just about anything else on the menu for variation.
Burger King: Usually go with the Big King, which I believe is now known as the King Supreme; it's their spin on the Big Mac. Lately, I've had a hankering for the Whopper with cheese. From time time, I will pick from a few other items on their menu as well, for variation.
Wendy's: Usually stick to the Big Bacon Classic here. Rarely get anything else off their regular menu. Sometimes they have special limited-time sandwiches which I'll usually try at least once, and if I like, continue to get as long as they have them. My favorite Wendy's special limited-time sandwich: the mushroom-cheddar cheese burger.
Arby's or Roy Rogers: Roast beef sandwich