The best gelato I've had in Florence was the Chocolate Mousse gelato at Veneta in Piazza Beccaria. I discovered it because I lived around that area when I was studying Italian. The walk from the Duomo to Piazza Beccaria is full of interesting, tiny food shops and clothing and kitchen boutiques that cater to locals primarily rather than tourists (of which there are relatively few because it's off the beaten track - there are no tourist sights in that direction). Vivoli was more expensive and nothing special, I felt, certainly nothing proportional to the raves in the write ups in the tourist guides.
