In case there are any sudoku lovers out there, I've recently discovered a similar type of puzzle called KenKen. You still have to have all the digits in each row and column, but instead of 9x9 boxes, there are groups of boxes that have to add (multiply, subtract, divide) up to a certain number. In the example I have below, each row and column has to have the numbers 1-6. The bolded lines show the groupings, and the number and mathematical sign in the upper left of each group show what number you have to get to, and how.

Fair warning, these things can be addicting ... at least if you're part geek like me.

If anyone's interested, I'll find and post some more.