A little out of the way but really good!
Just got back from Rome and wanted to share the best gelato we found: Giuffre. It's a bit off the beaten track at the southern end of Trastevere but its along the tram route so not too hard to get to. My son spent 5 weeks there for a summer class, lived two doors down, and went to this place every day. It was way better than any of the other places we went to in our trip and was almost exclusively locals plus all the students who lived near it. Its located at 255 Viale Trastevere - worth the trek if you're in Trastevere anyways. Like the better gelato places, the product is kept covered and buried in the counter, not open & visible. You have to go off the names rather than the appearance but they also offer 4 types of cream (plain, chocolate, coffee, & I forget the 4th) combined with your gelato- amazing!!