Hi,
check out the free Sudoku game at LunchBreakGames:
http://www.lunchbreakgames.com/php/game_entry.php?s_game=Sudoku&s_level=2
It allows to play 4×4, 9×9 and 16×16 Sudokus, featrues several difficulty levels, an advanced user interface and the possibility to save your highscore on our Web-Site.
Let me know what you think.
Cheers,
Tobias