Remember when you were in elementary school and your mom told you that the best way to memorize the planets (or any other list) was by making a song out of it? Creative departments at ad agencies remember that lesson. That's why they make jingles. But like all things, there are good jingles and bad ones. Good being those that stick in your head, making you hum them all day long; that make you remember what the jingle is selling; and that might even make you feel so good about the product or service that you decide to buy it. What are our favorites?