Sumdog
IXL
Multiplication Jeopardy
http://www.math-play.com/Multiplicaton-Jeopardy/Multiplication-Jeopardy.html
Sheppard Software
This site contains a series of games in PacMan, mahjong, quick click formats that enable students to practice skills such as converting fractions to decimals, fractions to mixed numbers, find algebraic values and solve geometry problems. You can compete against the clock or just practice using a pencil and paper to improve your math fluency and understanding.
http://www.sheppardsoftware.com/math.htm
Math Play
The math games on this website focus on several important topics such as adding, subtracting, multiplying, and dividing decimals and fractions, investigating algebraic expressions, computing area and volume of simple geometric figures, understanding the meaning of congruent geometric shapes and the relationship of the circumference of a circle to its diameter, and using percentages and circle graphs to interpret statistical data.
http://www.math-play.com/5th-grade-math-games.html