I would definately give Rome 3 days, for a big touristy city it has a good personality, and there is a lot to see. Must go to trastevere (In Rome)to eat, it is awesome
I am a fanatic about the sea, so I really enjoyed the coast towns, sorrento, and cinque terre were awesome. the whole almalfi coast is awesome. Also loved venice. Florence is cool but mostly its shopping and museums.
Another suggestion of mine is to go to some random small town and soak up the culture, if you are the only American (or foreigner, anyways) in the place, people really want to talk to you and you get to see the real country, not the tourist stuff. its more difficult to get around, but worth it.