Which ingredient in Italian bread gives it that great taste?
I'm assuming this is not a speciality Italian bread such as Panettone or Pan d'oro.  It's a regular bread loaf.

Hard to know for sure, but in all likelihood, the missing taste is due to short rise times and yeast type.  Most of the taste in bread is developed, not put in.

As suggested in the comments, the ingredients are bread flour (usually tipo 00 or 0), water, yeast, and salt.  Tuscan bread has no salt. and sometimes, there is olive oil to prevent the dough from developing a skin.  The notes below might be useful:


A French baker I work with, always keeps some of yesterday's dough and mixes it with today's dough.  This means an exponentially small amount of the dough can be years old.  He also performs three rises (two punch-downs).
Let your biga rest in colder temperatures for a couple of days so the enzymes can do their work and develop taste.
Get yeast from a baker.  The instant yeast at the grocery store is ok but the commercial yeast can work better with the longer ferments.  A famous natural bread baker in our area uses 2500 year old yeast from Egypt.  (the head baker has a heck of story on how he got his hands on this yeast).  Strict Neapolitan Pizza makers use Ischia starter for their dough.


Peter Reinhart explains Italian breads really well in The Bread Baker's Apprentice