Here’s a great web site for fans of Sudoku.

http://www.websudoku.com/

For the uninitiated, Sudoku is a Japanese puzzle game similar to a crossword puzzle, but with numbers.  The object of the game is to fill in the digits 1-9, one per box, so that each row, column, and region contains all nine digits, with none repeated.  It sounds a lot more difficult than it is.  For more information, refer to the Wikipedia entry for Sudoku.

http://en.wikipedia.org/wiki/Sudoku