http://www.quia.com/math.html
A page of JAVA Math games. Math games in topics ranging from addition of one-digit numbers to algebra and trigonometry. 

http://www.quia.com/mathjourney.html
Travel around the world by answering math problems. The journey begins and ends in London, and has stops in 30 cities along the way. To board the plane to each new city, you must answer a math problem correctly. If you get a problem wrong, you have "missed your flight". Miss three flights and the game is over. 

http://www.edu4kids.com/
Math Flashcards, Math Square Math Game, Math Tables Drill, Time Experience Drill, Money Experience Drill

http://www.coolmath4kids.com/
An amusement park of math and more -- especially designed for FUN, FUN, FUN!

http://www.algebra.com/
Use interactive solvers to get help and solve your homework problems. The site is organized along the lines of a typical school algebra program.