I love this Geometric Shapes chart shared by Kathryn on Kindergarten Kindergarten! I had to scroll down to find it, but found a ton of great ideas along the way. I also loved her shape museum. (She has lots of free ideas for teaching math concepts.
Math Task Cards for Early Finishers. Engage and Challenge your early finishers with these twenty details, multi-problem Early Finisher task cards! Your students will love completing these cards when they have finished their work or as extra enrichment.