I don't know whether you mean cocktail type sauce for meatballs or a marinara type sauce for meatballs with pasta or perhaps Swedish meatballs, but this holiday season I used this recipe for a simple, quick sauce, and heated it in the small crock pot with frozen pre-cooked "Homestyle" meatballs (which I cooked in the microwave according the package to speed things up). They all quickly disappeared:
Four ingredient cocktail sauce for meatball or little weiners
1 (8 ounce) can jellied cranberry sauce
3/4 cup chili sauce
1 tablespoon brown sugar
1 1/2 teaspoons lemon juice
These were offered as snack food along with a veggie tray, cheese and crackers, grapes, Christmas cookies, fudge, etc. while the family was gathered waiting for some of us to arrive and for the main meal to be served. I was afraid they'd ruin their appetites, but you can't over-estimate these appetites!
When I make my own meatballs, a trick I learned from a newspaper recipe one time that I find very handy is to pat out the meat mixture to about a 1 1/2" thickness into a rectangle, and then use a large knife to cut a grid. This helps you to make even sized meatballs quickly, and nobody minds if you just leave them square.