Some Fun Math Web Games    Click title to go to website.

Although this website has some advertisements, it has some good addition, subtraction, multiplication, division, and more:
 Sheppardsoftware.com
 Mathgames.com

A few other sites I like for multiplication are:
Meteor Multiplication,  
Pirates II Multiplication,
Penguin Jump, and
Multiplication 4 in a row (It's Connect four with multipication between moves.)