http://www.harcourtschool.com/

There are some good online interactive visual aids for math at
Harcourt's site,
http://www.harcourtschool.com/elab_subscription/menu_grade_select.html?grade=8
and grade=7, 6, 5, and 4.

Math Projects and Activities (to print) for Grade K through 8
http://www.harcourtschool.com/teacher_resources/math/activities.html