Multiplication Wheels - can easily be made with construction paper (or heavier cardstock) and brads. (The link to this site is blocked at school but you can access it from home or at the public library.make into addition or subtraction wheels
Calculating Pi with Real Pies - Numberphile - Published on Mar 2013 How accurately can we calculate Pi using hundreds of REAL pies? Extended version of this video will be uploaded to Numberphile on Pi Day - March
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.