Math Baseball for two players! http://www.funbrain.com/math/
Just like it says-Cool Math Games http://www.coolmath-games.com/index.html
Math Playground http://www.mathplayground.com/games.html
Multiplication Games http://www.multiplication.com/interactive_games.htm
Game Aquarium http://www.gamequarium.com/math.htm
This site has games in all subject areas and at all grade levels. Some of my favorites! http://www.mrnussbaum.com/mathgames.htm
This site has an Olympics game! http://pbskids.org/cyberchase/games.html
Lots of different games! http://www.surfnetkids.com/games/Math_Games/