US Mental Math Federation -- A not-for-profit organization to promote and encourage effective learning and teaching methods of mental math for early childhood and school-age kids.

The Math Forum -- A center for teachers, students, researchers, parents, educators and citizens who have an interest in mathematics education.

Pop Mathematics -- Interesting Math site, lots of interesting stuff..

Cut The Knot -- Interactive Mathematics Miscellany and Puzzles

Carol Hurst's Children's Literature Site -- Math Out Loud: Math and the Oral Traditions

Mental Arithmetic Drills -- Exercises in Math Readiness

Memory, mental arithmetic and mathematic -- Memory, mental arithmetic and mathematics