Simply wash whole tomatoes and pack then into plastic freezer bags.  When you want to use them, run hot water over the tomatoes until the skins crack, making peeling easy.  You can also add them still frozen to sauces, soups and stews, but you may want to remove the skins when they come to the surface. 

Conserve freezer space by cooking the tomatoes down into thick rich sauce before freezing.  Hold the spices and onions until you're ready to use the sauce because they lose their strength in the freezer.