I am looking for recommendations for a nice, affordable B&B for Sept.
I was looking for a B&B for Sept. but had dufficulty finding availability at any of the usual places recommended by Rick. I did find several available at cross-pollinate.com, the service offered by the American transplant couple who run the Behive. The Beehive is also an often recommended option. Their website is the-beehive.com. Also, you might try santasusanna.org if staying at a convent is of interest to you. That is what we chose - excellent value, clean, comfortable, safe, and an interesting experience. Good luck!
It's late to be booking a room during the high season of Sept/Oct. Try Nicolas Inn at www.nicolasinn.com, Gulliver's Lodge at www.gulliverslodge.com. If you don't have any luck try venere.com & laterooms.com
Nicholas Inn is tough to get into (but looks nice). We're staying at the All'Obelisco near the Spanish Steps. I would use a search engine like on Orbitz or Travelocity to see. Usually you'll get a cheaper rate by contacting the B&B directly through email on their site (and paying in cash when you get there). Good luck!
I suggest B&B Giovy near the Termini Station in Rome. I plan to stay there in November, so I don't have any personal experience yet. However, the reviews on tripadvisor.com are quite positive. See the links below. For other places you could do some searches on venere.com or tripadvisor.com.
Scott
http://www.hostelworld.com/hosteldetails.php/BBGiovy-Rome-7699
http://en.venere.com/hotels_rome/?ref=34990#o=default&r=0&m=0&n=giovy&f=T000100000000000&sb=1