Brainpop has instructional videos and games. Some are available to anyone and some require a membership. 

This website is among the resources recommended by North Carolina DPI.  It provides practice in many math skills.

Starfall provides practice in basic addition, subtraction, multiplication and division facts along with a few exercises in geometry and measurement. Look in the mathematics section and then click on any pictures that are in color. The other ones require a membership. 

Students can log in to quizlet to get extra practice with their math facts.