I use a weird combination of things. I dice up a green bell pepper. Then I combine a jar of Paul Newman's spaghetti sauce, and a jar of Ragu pizza sauce. I also put just a teaspoon full of mustard in with it. I just like the way all of that tastes together.
And i buy my meatballs. Rosina's Italian style frozen meatballs. Yeah, I know how to make them, but this way it's easy and the meatballs are quite good.