This was probably the best restaurant where I went in Rome.
I went there two times, and always ordered pizza, which is excellent and ENORMOUS! My favourite of all is the good old simple margherita, with mozzarella di buffala. It's really yummy!
Prices are very low, service is great and they are opened until very late - the first time I went there, it was around midnight, and they're open and working usually until 1 am.
The only disadvantage is that it's a little far from city centre, so if you're in center without your own car, it may be a little difficult to reach it. But if you happen to be on the area, give it a try!
Update: The last time I was in Rome, we ate there two times and it was delicious as always :) Certainly the best pizza in Rome.