Traditionally, coca-cola was made with sugar as the sweetener. More recently though, this has been replaced with high fructose corn syrup as a cheaper alternative.
However, some serious coke lovers say that real coke is only made with Sugar, and they try their hardest to get hold of this coke. Their answer? Coke which is certified Kosher for Pesach.
Corn (from which corn syrup is made!) isn't "chametz" - leaven food that is forbidden on Pesach. It is instead in a group of foods called "Kitniyot" - pulses. This includes some types of beans, peanuts, corn, and various other things. Jews from the Ashkenazi tradition avoid Kitniyot on Pesach, but Jews from the Sephardi tradition can eat them.
But to satisfy everyone, Coke that carries a "Kosher for Passover" label is guaranteed to be made with sugar. And these coke lovers will hunt high and low to buy it!
My source: A (non Jewish) colleague when I spent some time working in Atlanta, the home of Coke, telling me about some friends of his!