Sora Margherita at Lunch
Regretfully, I spent 2 days in Rome in May, and had only one decent meal. (Long story, but my advice is to NEVER ask your hotel in Rome for a restaurant recommendation).
I had lunch at Sora Margherita and really enjoyed it. Very inexpensive, and I thought the food was great. We just asked for a mix of stuff, and told them to stop bringing the food once we were full. They brought us the fried artichokes, some sort of pasta with a red sauce and tuna, and some sort of pasta carbonara.
Service isn't great, and I think I got yelled at once (but I think that's part of the whole experience).