Preschool Math with Counting Bears {free printable!} from Hip Homeschool Moms Has lots of other math and subject links for activities too

Kids - Math Making Patterns with Lego and Egg Cartons - The Imagination Tree

And Next Comes L: Simple Fine Motor Counting Math Tray {Fine Motor Fridays}

Two Preschool Math Activities with Duplo Legos {Frugal Fun 4 Boys} Math

Lego Math: How Many Legos Does it Weigh? could be a decent part game for the right crowd. choose interesting items to weigh.