Kenken is a logic puzzle game similar to Sudoku, but players are given + - x or ÷ questions to solve the area and complete the grid. This site has a range puzzles at various complexities and difficulty levels.
http://ictmagic.wikispaces.com/Maths
My students love this website and especially this game. I thought it was just a silly game at first, but it is actually pretty good for puzzle solving, etc.
Cool Math is a game playing website. Most games require players to display logical and mathematical thinking to pass through game levels. No subscription is needed to access this site.