K-2nd Grade

Clockwise-practice telling time
Time Quiz--take a quiz on your clock reading skills
Base10 Blocks--virtual manipulatives
Math Magician--practice addition facts
Virtual Manipulatives--
Fractions--name that fraction interactive
Baseball Addition--practice addition facts
Lemonade Stand--math and economics involved in owning your own stand 

3rd-5th Grade

Think Through Math--practice math skills (unique log-in/password from teacher)

A+ Math--flash cards, games and homework help
Cool Math4Kids--online math games