Stay away from Naples!

OK, that's the simplified version. The longer version is go to Naples only if you're interested in banging some Italian prostitutes. Aside from Naples, I'd say the destinations kinda depend on what he/she wants to do. I'll try to break it down into a few categories

do not come home without seeing this:

• all of Venice
• David by Michelangelo (in Florence)
• St. Peter's Basilica (if you're Catholic)

sweet places to hang out and meet folks:

• anywhere in Florence
• Venice's St. Mark's Square
• Sienna's main piazza (square)!!
• Sorrento, extremely beautiful and very much like Cinque Terre but more developed

outdoors/nature/scenic/hiking:

• Cinque Terre
• Lake Como/Dolomites (never been but I've read about it)
• Lucca (bike the ramparts)
• Almalfi Coast - The A-coast as I like to call it (just made that up :P) includes Amalfi, Sorrento, Positano, Ravello, etc. Mostly a driving adventure, a lot like Big Sur and Highway 1 in California.

big museums big churches galore:

• Rome
• Florence

pottery/Italian majolica: Deruta/Orvieto

surprisingly skippable:

• leaning tower of Pisa
• Milan
• Pompeii

Buy gelato everywhere you go. Do not skip an opportunity for gelato because you will miss it when you come back home. For the engineering/science types, I recommend reading Brunelleschi's Dome and then visiting the Duomo (dome) in Florence to see it in person. Very amazing.

Finally, I really like Rick Steves' guide. He does PBS specials on European vacations and puts out a travel book each year for several countries. He also has a website: http://ricksteves.com/plan/destinations/italy/italy_menu.htm. He saved us some major $$ when picking out places to eat and sleep.