I just got back from Italy yesterday. We stayed in Milan and did day trips to various cities. Granted, we didn't spend a whole lot of time in each place, but we got enough of a taste to get the feel (and definitely want to come back again).
We booked a tour that drove use from Milan to Cinque Terre. That was really nice since we didn't have to worry about transportation. We would have enjoyed it more, but weather was less than ideal (it was cloudy and rainy). Because the water was so choppy, we could not do the boat excursion part of the trip. However, it was a nice place to go to and I would love to go back and check out each individual cities more in-depth. Pesto is big there, so you might want to try a dish with pesto to get the local flavor. We ate at Pae Veciu in Monterosso al Mare.
We took the train from Milan to Verona since it was a short trip out there. One of my friends wanted to check out Casa di Giulietta. It's admittedly a tourist trap. If you decide to check it out, I would recommend going there early since the place is just a little courtyard that people cram into. If you plan on checking a bunch of things out in Verona, I would recommend looking into the Verona Card which can save you money on various attractions.
In Venice, we decided to take a nice slow boat ride around the grand canal. That took about an hour to get to Piazza San Marco. We took a faster boat (25 minutes) back to the train station. We did not do a gondola ride this time, but I would definitely do it the next time if I had more time.
In Florence, we did a hop on/hop off bus ride. I think that was the best value if you just wanted to sit and enjoy the views of the city. They also provide you with headphones so you can listen to the history behind some of the landmarks you will pass. There are two routes. The red line takes you farther out to Fiesole. As with all hop on/hop off buses, you can get off at any stop, explore a bit and catch the next one. The routes also take you to the Piazzale Michelangelo, so you can see a panoramic view of Florence. Before leaving Florence, we wanted to try Bistecca Alla Fiorentina. We ate at Il Portale which is close to the train station.
If you haven't considered it, I would recommend going to Lake Como, as well. It's beautiful up there.
Admittedly, Yelp was a good reference for finding restaurants in the area. I also had a Kindle version of the Italy books by Rick Steves and Lonely Planet on my phone.
If you want to have a tour do all the planning for you, I recommend Zani Viaggi and Viator for booking.
Hope this helps!