Well, here is another use for them–a shape book for your preschooler!
Just mount index cards with pictures of different shapes and let your child add to their book as they find new shapes lying around the house. Mail, magazines, catalogs, and foam shapes are great additions! Plus, if your child is proficient at using scissors, it provides great cutting practice!
You can do the same thing with colors, letters, and numbers too! The possibilities truly are endless. :)