There are many reasons to substitute light corn syrup. You can replace one cup of corn syrup with one of these simple substitutes:
Which Substitute Will Work Best in Your Recipe?
Corn syrup doesn't add flavor to a recipe—just sweetness—so sugar is definitely the best substitute, in terms of flavor match. But, unlike corn syrup, it crystallizes at high temps, so it's not a good choice for candy recipes that you have to take past the softball stage (235 degrees). It is, however, tops for pies (like pecan).
Any maple-flavored syrup is a brilliant substitute in all situations, assuming your recipe can take the addition of maple flavoring. It's made from corn syrup, so really you're just substituting like for like when you go this route. Of course, this won't seem like a brilliant substitute, if you're allergic to corn or trying to cut corn syrup from your diet.
Honey is a good stand-in in baked good recipes. It'll keep them moist, just like corn syrup. While the honey will add a bit of flavor, the difference will be subtle, as long as you stick with light-colored honey.
Agave syrup has a fairly mild flavor, so it's another option to consider. It can be used in pies, sauces, and other dessert recipes, but won't work for candy making.
Light molasses is perhaps the substitute of last resort. It'll give you the body you're after, but it'll change the flavor of your recipe more than any of these other substitutes. Avoid using blackstrap molasses at all costs. It has a very distinct taste that is likely to overwhelm the other flavors in your recipe.
If you're making a candy that has to go to the hard ball stage, corn syrup, brown rice syrup or another glucose syrup (see below) really is the best way to go. But hard candies were made long before corn syrup existed, so consider consulting a vintage cookbook for techniques, if you're determined to forgo corn syrup entirely.
If you live outside the United States and haven't been able to find corn syrup locally, glucose syrup (also known as confectioner's glucose) or golden syrup can be used in its place. In fact, corn syrup is just a type of glucose syrup. It can also be made from potatoes, wheat, rice, and a few other things.