http://www.mathblaster.com/parents/math-games/4th-grade-math-games
(Online math games)
http://www.toonuniversity.com/free/math-games-4th-6th_a.asp
(Math games to increase speed and accuracy with facts)
http://www.math-play.com/
(Various games)
http://www.learninggamesforkids.com/4th-grade-math.html
(Games to practice math comprehension)