Diego's place comes highly recommended.
If you're more than 2 persons staying there (and you can be, no problems at all) it's a steal. It's clean, spacious and with great AC.
The Roma Metro is just across the street, use it, it's fast, cheap and within 10-15 minutes you're at Roma center (Piazza di Spagna, Pantheon or Termini).
And within 3min walking distance in the other direction, you have a huge supermarket with great opening hours, and, should you wish, a McDonalds.
Top notch!