I love making meatballs in advance. When I had the teenage boys living with me, I would buy a huge pack of meat and cook them all up as meatballs and freeze them. The boys always thought it was heaven when I made anything with beef -- sometimes, I miss the boys!
I still do it, now that it is just our family, but I need to start making the packages smaller.
I always browned mine and then froze them in tin foil and a zip lock storage bag.