Barcelona...Look at the Jazz Hotel for a night or two. Walk the Las Ramblas and stop in at the Mercado. Do the HOHO bus..a great option.
Nice..Even though we don't like cruise booked excursion we booked one for this port that went to Nice and Monaco...turned out great.
Florence..See if your ship has a DIY shuttle bus that will drop off/pick up at Santa Croce square. This was just amazing for the transportation and time on our own.
Pisa...Meh.