I've been to Italy twice. It's wonderful.
I didn't go on a guided tour, but I have a friend who speaks a little Italian and likes planning trips. She planned both itineraries, with a lot of help from travel guru Rick Steves.
The first time, we stayed in Rome, Florence, Siena, the Cinque Terre, Venice and Milan. The second time, we stayed in Montepulciano, Florence, Rome and the Amalfi Coast.
My favorite places were Rome, Florence and Positano on the Amalfi Coast.
Pisa seemed skippable. We went past it on the train.
I'd also recommend getting some Italian CDs and listening to them in your car for a while before you go. Not essential, since many Italians speak English, but helpful.