(For D&D 4th Edition)
I rarely use published monsters, preferring to come up with my own things for my players to fight in our own homebrewed world. 4e is great about this, making it really easy—Monster Manual 3 really streamlined monster creation, and the MM3 on a Business Card gets extensive use in my games. There's only one thing missing from it... and that's the generation of ability scores.
Now, ability score generation is USUALLY not important, but every once and a while I need my monsters to engage in opposed skill checks with my players. I can always just wing it, but it'd be nice if I could grab a quick formula for a recommended amount.
Furthermore, MM3 on a business card doesn't give a formula for Perception, or Initiative, and both of these do come up rather often. If there was a formula for ability scores, then these two items could also be derived pretty easily.
In the end, it doesn't really impact my games THAT much, and if I have to eyeball it and make up numbers that feel right compared to my players at the time, I'll do that. But is there such a formula?