The New York Times this weekend started running a new numerical logic puzzle from Japan called KenKen next to their crossword puzzle.
It's sort of like sudoku, but with math involved. I found this web version of the game that lets you play online and get your solutions right away, without having to wait around for the New York Times.
KenKen was developed by Japanese teacher Tetsuya Miyamoto, who founded the Miyamoto Math Classroom in Tokyo. Miyamoto uses puzzle solving about 90 minutes a week in his classroom.