Our favorite in Rome was in Trastevere. The restaurant is Spirito Divino, located at Via dei Genovesi 31 (cross the Ponte Garibaldi, hang a left in front of McDonalds). You can read more at my still-unfinished trip report (search for "a short thesis) and it will pop up.

Great food, outstanding service and a reasonable price. Wonderful wine list.

We also at a del Pallaro...good price, decent food, and a lot of fun.

Osteria dell'Antiquario - Piazzetta di S. Simeone 26/27, Via dei Coronari. Phone 06-687-9694
This is wonderful Roman food in a very relaxed and romantic setting. You're likely to be the only tourists. Try to reserve a table outside in the (very quiet) square facing the fountain.

Has anyone eaten at Antica Pesa?