Yes, plain old cornstarch.
In addition to making fondant less sticky and thickening soups and gravies, cornstarch makes an awesome candy mold. All you have to do is pack it in a pan, press your shape of choice into the starch, and pour in your candy filling. The cornstarch does a great job of holding the shape and making custom candy molds, and the best part is, you can re-use it endlessly, and then bake with it when you're done.
You can see a cornstarch mold in action in this recipe for Marshmallow Easter Eggs. I use a large soup spoon to make egg shapes in the starch, then pipe in some loose marshmallow filling. After a setting period, I have egg-shaped marshmallows--no fancy mold required. Check out the photo tutorial showing how to make these eggs for full details. This method also works really well with gummies, jellies, and other soft candies that are difficult to mold in traditional ways.
Marshmallow Easter Eggs Photo c2010 Elizabeth LaBau, licensed to About.com, Inc.