National Library of Virtual Manipulatives
Pattern block manipulatives
Base 10 blocks (with 100s chart)
Virtual Dice - 6, 8, 10 or 12 faces
Interactive clock (great for elapsed time!)
Addition and subtraction of decimals
Fraction bars (fractions, decimals and percents)
Cuisenaire rods
Geoboards
Attribute Blocks
Tangrams or PBSKids Tangrams
Pentominoes
Interactive spinner
Make your own graph
The Pythagorean Theorem
The Value of Pi