Out of Florence, I highly suggest doing a day trip (better take 2) to Cinque Terra. Fantastic, unique scenery. Take the boat if you can.
If you've got the time, ie. a day, this is a must. Cinque Terra is an UNESCO heritage site and incredible land. I don't know about now, you should check it out, but I heard they had floods and a lot of the tunnel connecting the small towns may not be open. Beautiful, serene, simple life in those five villages. Pisa is close by, but they only have the leaning tower IMO. In Florence, besides the above mentioned, gold and leather are great buys if you keep your eyes open. Got some great deals on shoes. Ponte Vecchio is the oldest bridge in Florence and full of jewellery shops, nice views down the Arno river. Never pay full price, always haggle, it's customary. Some incredible churches, they're massive, ie. The Duomo, Santa Maria Novella, Medici Chapels, etc... Lots of Architecture and Arts throughout the city, walk around the core.
Venice is very interesting. Gondola ride is always a great time, walk around the core, nice little shops throughout, the Rialto bridge is a must see, especially at night when it lights up, Piazzo San Marco is the main square with a large church, Doge's Palace, Campanile and several museums including the Googenheim Museum, as mentioned above the tide might be high as the Piazza is the lowest point in Venice but they install short wooden scaffold to walk on to keep dry and watch out for those pigeons, lots of them in the piazza. Again lots of churches that are spectacular. If you have time, grab a boat to the islands of Murano and Burano for glass art and lace, if that's your thing.
Love these two cities, actually love all the cities in Italy, visit there regularly, fascinating country. Good luck and have a great trip, oh, don't forget the digital camera and take lots of pix.
