Two of my favourites are:
HV Morton's "A Traveller in Italy".

The Stones of Florence, McCarthy, Mary McCarthy, Paperback, Book, ISBN: 0156027631

Empires-The Medici: Godfathers of the Renaissance.

Angels and Demons- Dan Brown :)

And this is really not on the novel front...but the next time you are in Barnes and Noble, head over to the European travel section and pick up a DK Eyewitness Travel Guide for one of your cities.. I have them for Florence, Venice and Rome. They are awesome! I guarantee you will love them and take them with you on your trip. They are visually appealing with 3-D maps of city sections and have interesting facts (historical/religious/architectural, etc) for almost everything you might want to see.

Have fun!