Khan Academy- a collection of math videos from basic math to advance.  They have also added self-paced lessons with activities.

http://www.khanacademy.org/

Johnnie's Math Page is the site to find fun math for kids, math games, and even a little math homework help.  Interactive math activities from across the web have been organized by topic to make math learning enjoyable and interesting.

For parents and teachers, you will find math lessons and math worksheets as well as links to other math teaching resources.  For those who like a challenge, you will find free math games in the math puzzles section. 

http://jmathpage.com/

Practice math facts, solve math problems and practice your counting skills.

http://www.playkidsgames.com/mathGames.htm

Just mathfacts!

http://www.playkidsgames.com/games/mathfact/mathFact.htm

Free online math games for kids. 28 different kinds of games on Addition, Subtraction, Multiplication and Division that teach basic and advanced math.

http://www.sheppardsoftware.com/math.htm

Math Run is a simple and fun game for practicing math skills. Math Run presents players with a scrolling series of mathematics problems. The players respond to each problem by using the right and left arrow keys on their keyboards. If a problem is displayed with its correct answer press the left arrow and if the wrong answer is displayed press the right arrow. The game begins with simple addition problems and gets progressively more difficult as players advance through the levels.

http://mathrun.net/

"Kids teaching kids" videos of math concepts!

http://www.mathtrain.tv/index.php

Practice Geometry!

http://www.compasslearningodyssey.com/sample_act/math3_4/MA3CA05a-package_preloader.swf

http://www.xpmath.com/forums/arcade.php?categoryid=5

Try these websites to improve your math facts!

Ultimate challenge! http://www.oswego.org/ocsd-web/games/Ghostblasters1/gbcd.html

http://www.learnyourtables.co.uk/

http://letsplaymath.wordpress.com/free-mostly-math-resources-on-the-internet/

http://tutoring.sylvanlearning.com/newsletter/0704/math.cfm

http://www.coolmath4kids.com/

http://www.linkslearning.org/Kids/1_Math/2_Illustrated_Lessons/index.html

http://www.learningplanet.com/act/mayhem/index.asp

http://www.mathplayground.com/games.html

Practice your math facts (addition, subtraction, division, multiplication.  For Grades 1-6.

http://www.wildmath.com/playset.htm

http://www.funbrain.com/math/index.html

http://www.classbrain.com/artgames/publish/math_games.shtml