I've been doing these puzzles lately, and I'm hooked. They're really addictive, especially if you like things like crossword puzzles and the like.
Above is a link for anyone who wants to know what Sudoku puzzles are. Try out the sample and see if you like it. They are not as easy as they look- especially when you first start.
And here is a link to a page that has 3 free daily Sudokus- easy, medium, and hard.
And this link is Sudokus for kids. A great way for them to learn logic. My 6 year old is doing them, too.
Have fun and enjoy!