We were married in Florence. Here are a couple of good ones. Not sure how much you want to pay though.
Villa la Vedetta (absolutely spectacular) - not sure about now, but this was the only Michelin starred restaurant in Florence.
JK Place (gorgeous)
Grand Hotel (ask for a newer room)
Hotel Lungarno (LOVE this place)
Villa la Massa is a sister hotel to Villa d'Este in Lake Cuomo. It's very nice but located a little outside Florence proper. They have a van that will shuttle you back and forth. Because its not in the city proper, the rooms are a little bigger/nicer.