Some other places worth noting
Naples: Naples is dirty and crowded, but it has good food (it's the supposed home of pizza). Vesuvius provides a nice view and Pompeii and Hercolaneam are good for a history fix. For the military traveler, there are regular flights in/out of Capodichino, which doubles as a US base and the Naples Airport. If you're time-limited or want to keep in a smaller area, I would skip Naples itself. You can get a better South Italy experience in several other places.
Amalfi Coast: Beautiful. Positano is the only town I've stayed in down there, but I've seen a good chunk of it from sea and air. It's small, cute, and relaxed. There's fantastic seafood (eat at Da Adolfo) and it's the home of Limoncello. Positano is awesome. Google pictures. If you go there, you're likely travelling through Naples. It's a short trip from Naples down to Sorrento, and along the coast. In the right weather it's a beautiful drive along the ocean.
Modena/Maranello: I'm a huge car nerd, so if you want your Ferrari fix, I can recommend this. Modena is also the home of balsamic vinegar, so you can do tastings and tours there just like the wineries in other parts. There are two Ferrari museums, one at the factory in Maranello, and one in Enzo's old garage in Modena. It's also really easy to rent one and tear around the countryside. I rented a 458 for an hour (500 euro) and it was well Worth it. Bologna is home to Lamborghini and Ducati if that's more your thing. The Whole pianura, or the Po river valley, geographically speaking, is rather bland, so don't expect lots of pretty hilltop castles and Tuscan-style villas. It's the industrial heartland of Italy.
Milan: Never been, but I know a lot of people who have. It's got a duomo and is the mecca for high-fashion if that's your bag. I don't really have any desire to go for whatever that's Worth. On the plus side, it's near Lake Como, so it makes sense as a connection.
Puglia: This is the "heel" of the boot and the region I live in now. It's largely 'undiscovered' tourist-wise, but a great place for food and beaches. The food down South is much simpler than the heartier dishes from the North. Fewer ingredients, but lots of flavor. You have some of the best beaches in Italy - this is where many Italians travel to during the summer - both on the Adriatic and Ionian. The Gargano peninsula (the spur on the heel) has tons of beaches and caves along the water that can only be explored by boat. Rent a gommone (RHIB) and wander the coast. There are a ton of little towns dotted all over that each have their own particular charm (Matera, Polignano a Mare, Otranto, etc...), but are not as tourist-centric as some of the major cities, and therefore great deals. The South is much more agrarian than the North, so it has a much more lax lifestyle and is a little poorer and less modern than other zones.
Sicily: Taormina is cool and has fantastic views. Siracusa is a cool little seaside city a bit further South down the coast that has a lot of ruins and is good to checkout if you're in the area. Noto is a cute little city that does this crazy flower festival in May (?). Catania is a big city, but has a giant fish market and some good areas to check out on the waterfront. Palermo, outside of the main piazzas, is dirty and sketchy as hell.
Sardegna: Most beautiful water I've ever seen. Porto Cervo is on the northeast coast along the "Costa Smeralda" and nearby some Island nature preserves that are well Worth checking out. Porto Cervo itself is EXPENSIVE as hell, but it's easy to stay outside of it for a lot less. Rent a boat and sail around to check out all the Amazing water and beaches. I can't emphasize enough how Amazing the water is there.
(part 2 of probably 3)
Back in the day, we saw some red Ferrari screaming around and around a track - chased it at 1,000 ft in the Phrog (couldn't catch it...)
Thoughts on Lake Como?