Gelato in Firenze
The best gelato in Florence is generally agreed to be Carapina, on a small alley not far from Ponte Vecchio.
Other great ones include:
Gelateria Santa Trinita
Grom is ok, but these others are much better, and not part of a chain
Another you should make an effort to go to is Il Re del Gelato, not far from the train station. It's run by a real chef who crafts truly incredible flavors. He's from Sicily, so you can also have your gelato stuffed into a soft sweet bun instead of a cone.
For chocolate flavors stop by Vestri.