Subtract 1- or 2-digit number from a 2-digit number with/without renaming
As a middle-school math teacher, I have seen many students who do understand abstract concepts, and even enjoy learning about things like Pi and the Pythagorean Theorem, but who appear to be unable to do so due to a weak grasp of math fundamentals.
It is amazing the difference in effort you will get from worksheet to worksheet. Granted the amount of effort may vary immensely from year to year depending on the group of students you have.
Granted, that will always be a tough uphill battle for math to win out over most video games, but the point is, students today are much more immersed in technology than ever before. So even if you need to pass out a math worksheet to review concepts and formulas, it will greatly benefit your cause if you design the worksheet to be as stimulating as possible.