There are several great deals today out of San Francisco including $427 round trip SFO to Rome with American and British Airways on BA coded flights. Low fares are for travel March to May. The $427 ticket price is through online travel agencies found in Momondo.com searches.
Google Flights SFO-Rome low fare dates are a good start for locating dates to search through Momondo.com.
Kiss&Fly.com San Francisco SFO – Chicago ORD – Rome FCO – London LHR – SFO