Scott Foresman Successnet - Math Book Online! Great Activities! http://www.sfsuccessnet.com
National Geographic for Kids http://www.nationalgeographic.com/kids/
Very fun site! This has widgets! http://www.iknowthat.com/com
Interactive Grade Level Skills http://www.internet4classrooms.com/grade_level_help.htm
Funbrain.com - Fun Math site! http://www.funbrain.com/