This seems to be very popular, probably as much because of the simplicity as the taste.

Place prepared (cooked) meatballs in slow cooker. Combine two 12oz jars of Heinz Chili Sauce and one 32oz jar of Grape Jelly in saucepan and stir while heating. When mixture is uniform, pour over meatballs and set slow cooker to low; allow to simmer before serving. Viola!