In a tomato sauce recipe, how can I cut the acidity? It seems that every time I make a tomato sauce for pasta, the sauce is a little bit too acid for my taste. I've tried using sugar or sodium bicarbonate, but I'm not satisfied with the results.
My secret weapon is onion. Caramelize the onions first.  This creates a natural sweetness.  Always use ripe tomatoes; if you cannot then use canned.  The canned are made from ripe tomatoes and tend to be a very good substitute.

Also, the celery and carrot suggestions are very much a good addition - you are making a classic tomato sauce when you include the celery and carrots, 1 part each celery and carrot to 2 parts onion.  Add the onions first to get the caramelization.

I don't get too fancy with herbs, usually one good fresh herb does it for me, basil or sage are two favorites of mine.

There is a suggestion to add cream, why not use the parmesan end you may have in your fridge, it is dairy and allowed to slowly simmer in the sauce will lend a very nice flavor note.

Acidic sauces are usually reserved for nights when I make a puttanesca sauce - it goes with the capers and calamata olives I add to it.

Don't forget to season with salt and pepper.