A+ Math @ http://www.aplusmath.com/

This site has plenty of activities and games to help beginning to intermediate math students improve their skills. Flash cards, concentration games, more.

AAA Math @ http://www.aaamath.com/
Designed for grades K-8, this comprehensive math resource contains hundreds of pages of basic math skills and randomly-created interactive practice activities.

Ask Dr. Math @ http://mathforum.org/dr.math/

This is a huge resource of answers to math questions for elementary to college students. If you have a question not covered, you can ask Dr. Math!

Brain Bashers @ http://www.brainbashers.com/

Includes an interesting collection of math, logic, and language puzzles, games, and illusions, seperated into easy, medium and hard categories.

Brain Teasers @ http://www.eduplace.com/math/brain/

Brain Teasers presents a weekly word problem for 3 grade ranges; answers are given the following week. A section with past 'teasers' is also available.

CoolMath.com @ http://www.coolmath.com/

Have fun while practicing your math through lots of cool games, activities, and animated demonstrations. Includes coloring pages for young kids, and helpful sections for teachers and parents.

Funbrain @ http://www.funbrain.com/

Math games for all ages. Games include Math Baseball, Power Football, Change Maker, Fresh Baked Fractions, Line Jumper, and Shape Surveyor.

Math.com @ http://www.math.com/

Math.com offers a lot for everyone. Students can find homework help, puzzles, online calculators, and more... teachers can take advantage of lesson plans, classroom resources, and career resources... there's even a section for parents with lots of helpful information.

Math Advantage @ http://www.harcourtschool.com/menus/math_advantage.html

Math activities and games for grades K-8. Some of the games require that you have the Shockwave plug-in.

Math Goodies @ http://www.mathgoodies.com/

Lessons and exercises for a variety of math subjects. Includes calculators, puzzles, and MathChat message boards where you can ask questions and share ideas.

MathStories @ http://www.mathstories.com/

Includes over 1,000 math word problems for grades 1 through 6, plus instructions on how you can use numbers to do magic.

Prongo @ http://www.prongo.com/

In the mood for a fun collection of games that might just teach you something at the same time? Practice your math skills in games like Lemonade Larry and Batter's Up Baseball. Also includes age-specific games like checkers, connect the dots, matching, word and maze games.

Rick's Math Web @ http://www.ricksmath.com/

Pre-kindergarden to high school students looking for a better understanding of math will find over 4,750 problems to help them improve their skills. Problems can be printed in worksheet form and tips and tricks are included for each area of study.

Teach R Kids Math @ http://www.teachrkids.com/

Learn number basics, addition, subtraction, fractions, and much more with these interactive online math worksheets. Exercises are designed for preschool through 3rd grade students.