Homework help from Dr. Math http://mathforum.org/library/drmath/drmath.high.html
Interactive Math Puzzles http://www.cut-the-knot.com/games.shtml
Geometry from Dr. Math http://mathforum.org/library/drmath/sets/high_geom.html
Edhelper provides worksheets to reinforce mathematics topics http://www.edhelper.com/
Sudoku provides puzzles with different types and difficulty for the new craze of Japanese puzzles http://www.sudoku.com