Our hotel in Florence recommended we have dinner at Trattoria ZaZa. If you come by 6pm, which is very early for Italians, you can avoid the long queues seen in this photo.
ZaZa offers excellent Tuscan cuisine in spacious surroundings with excellent service at reasonable prices and no tips expected.
We went there nearly every night of our stay in Florence, early so we didn't need to queue. We were surprised to hear they seat about 700 quests.