Drain, drain, drain. A greasy spaghetti sauce is just nasty. Line a colander with three paper towels, one on top of the other, and place the colander over a pie plate or other dish. Put the hot ground beef in the colander and press another paper towel over it to help the fat drain out. Also, wipe out the inside of the cooking pot so it won't be greasy either. Let the meat drain for at least five minutes before adding it back to the pot. You can even make up the rest of the sauce except for the meat and add it last.
The meat will still have plenty of fat for flavor, but there won't be that sheen on the surface, and your family will rave over your spaghetti sauce.