Exploring the city centre in the carriage is the most romantic way of course. Slowly and very comfortable it allows you to take the pictures during the ride. Besides, the coachman is very helpful in giving the informations regarding spots you're passing by. Though, it wont take you to Belvedere and across the Ponte Vecchio.
If you have money (I don't know prices but I believe it's not that cheap) and time, you can tour Florence by horse coach. I guess it's a nice thing... and it's very classy! :)