I always make my own marinara sauce. Many may think that it's too much work to make your own but it is surprisingly almost as easy as opening a jar. Here's my favorite way to prepare marinara.
1 28oz can of crushed tomatoes (I prefer Cento Brand because they aren't from concentrate and the tomatoes taste so fresh)
1 small onion, chopped
3 cloves garlic, chopped
1 tbl basil
2 tsp salt
2 tsp sugar
In large pot saute the onion and garlic in a small amount of olive oil until tender. Add the can of the tomatoes (swirl about 1/4 cup water around the can so you get all the tomato out), add in the rest of ingredients and simmer until hot or on low for as long as you like. The longer it simmers the yummier it gets (and the better your kitchen smells)!