YACOMR: Yet Another Collection of Online Math Resources. The purpose is to make available the resources that I have vetted and identified as useful, fun and otherwise valuable.
Figurative numbers, finite differences and formulas from MATHGYM. Good for simply finding patterns or using tables to derive formulas.
Pythagorean Triples from Saltire. Exploring when Pythagorean triples occur using Java. Would be good basis for Geometer's Sketchpad project.
Cookie Sharing from The Mathman. Children discover infinite series.
Morse Code as Binary Tree. Includes audio options.
US Debt Clock. Oodles of real-time data about the financial condition of the US.
The Science of NFL Football from NSF. Vectors, parabolas, geometry, nutrition: videos with NFL Players demonstrate the math and science.
Henri Picciotto's Math Education Page. Comprehensive K-12 math topics mapped by grade or subject.
Distributing and Factoring Using Area from NCTM Illuminations.
Nets for 3D objects from WisWeb.
Math Doodling: Binary Trees from Vi Hart. Makes child play of Sierpinski's triangle, cellular automata and binary trees. She also has photos of food used to create geometric shapes (including Sierpinksi's triangle.)
National Library of Virtual Manipulatives (NLVM). Great set of applets to explore area model algebra, base ten blocks, signed interget operations and more.
Cynthia Lanius Math Lessons. Recommended: Fractal Geomtery and Volume Functions.
Popcorn cylinder problem from Figure This! Challenges.
Egg Carton Fractions from Utah Education Network. Also, Fraction Concepts with Egg Cartons from Paul Griffith's Math Models - using models to visualize math.
The Math Page: Self-paced and well-explained lessons from arithmetic through algebra, geometry, trigonometry and calculus.
Gamequarium: home to Billy Bug and Banana Hunt - fun games to practice the coordinate grid and estimating angles.