You can also chop up some mushrooms, any kind you like from button, to shiitake to portobello, chop them up pretty fine and then sautee them until they just start to brown, in a little bit of olive oil and some chopped onion. Then stir them into your sauce. Super yummy.
Or if you like a more of a creamy style sauce, simply add some real cream to your marinara sauce. Or if you like a cheesier flavor, you can also add cream cheese. Yum! If you’re worried about the fat content, you can get low fat versions of the cream and the cheese and it won’t even make a difference in the taste, just don’t use the fat free stuff, which does change the flavor considerably.