There have maybe been 50-100 or more discussions here of Italian restaurants in the past 6-12 months. It would be worth your while to do a "Search this board" search to find some prior threads.
Some of the better regarded Italian restaurants in SF include Da Flora, Ideale, Milano, Antica Trattoria, Osteria del Forno, Incanto, Delfina, Perbacco & Acquerello.
A lot depends on what type of Italian food you are looking for and how much you want to spend.
Italian Italian? Cali-Italian? Northern Italian? Southern? Sicilian? You'll get as many opinions as you want.
My daughter and her boyfriend went to Pizzaiolo last Saturday night and LOVED the food, even more than Incanto the night before (husband and I went there too and found the food a bit too salty. I also find Oliveto over-salted frequently and wish they would let the diner add more if they wish to.)
La Cicchia is one of my favorites.
My Italian friend (from the Marche) says Riva Cuchina in Berkeley is most like food in Italy: lighter and purer flavors. I spent all of two weeks in Italy total, so I'll have to bow to his opinion. I do like the restaurant a very great deal.