These sites require a fee, unless your school already has a subscription.     This site is organized by grade levels and subjects.  Site contains games, videos, and etc. using various online multimedia.  Available for purchase both by parents, teachers, and schools.

IXL Math     Log in to practice math skills listed by state standards.  Available for purchase monthly by parents or by classroom or site license by teachers and school districts.

Study Island    
Log in to practice any subject and any standards.  Teachers & parents can check progress online from any computer with internet access.

Math Stories       Math Word Problems (math problem solving and critical-thinking skills)

KB Teachers       Contains a variety of activities and worksheet generators for several subjects.