I remember ketchup and BBQ sauce being the most frequent choices (and sometimes the only advertised choices), although they don't have to be: my DH, who likes to order chicken fingers himself, would sometimes ask for a side of some other, "non-traditional" dipping sauce that appeared elsewhere on the menu -- Buffalo sauce advertised as coming on a sandwich, or creamy ranch dressing shown on a salad -- and CMs were always happy to oblige. Obviously, the availability of alternative sauces and dressings will vary depending on which CS restaurant you visit...