When tomato season is in full swing like it is now, you should feel free to use fresh, ripe tomatoes for the sauce instead. Marcella Hazan recommends two methods, as found here (courtesy of Smitten Kitchen):
Blanch: Plunge the tomatoes in boiling water for one minute. Drain them and let cool, then skin and slice into coarse pieces.
Puree through a food mill: Cut the tomatoes in half and place in a saucepan over medium heat. Cover and cook for 10 minutes, then transfer to a food mill fitted with the largest holes. Puree through the food mill into a bowl.
Once prepared, use in the same way as the canned tomatoes, written above.