We did Istanbul on our own. It was very easy to find the blue mosque and once you've found that all the other sights were right beside it. We walked (about 40/45 minutes) from our ship by following the tram lines. Trams are very frequent and leave you directly at the mosque if your not into walking. Istanbul is truly beautiful.
As we had already been to Naples and Pompeii we decided to go to Sorrento or Capri. The ferry terminal (molo berevello)is actually visible from your ship. It is just left of the cruise terminal. You can buy tickets easily there. We just missed the 9:50 boat to Sorrent so we got the 10:05 ferry to Capri instead. It was incredibly beautiful and so easy to do ourselves. In fact it would be very easy to spend a few hours in Capri and then get a ferry from there to Sorrento before getting a ferry back to Naples.
This was an excellent tour and fantastic value for money. Although it was Pisa and Florence on your own you get a map and all the history of the main attractions before your guide leaves you. Also Florence is very compact so it is very easy to walk around.