Venice, Florence, Sorrento and Rome: Passes for anything?
 

I am traveling to the stated cities in June. Do I need to purchase any passes (museum, vatican, etc.) ahead of time. If so, what is the best way to do this? I've read mixed reviews of trying to buy these from the U.S. Is it better to wait until we are in Italy?

Yes is the answer.
Get online tickets to everything you can in advance.
No sense to spend valueable time waiting in a line.

If you want to visit the Scavi (excavations under the Vatican), you need to make arrangements in advance, but if you mean THIS June, that ship has sailed. I believe you still have time for a booking for the Uffizi, but as it will be high season, you may be out of luck for that, too. But the lineups aren't too dreadful if you plan strategically...search the board for specifics for those museums you are specially interested in.

For Rome, I suggest the Roma Pass (23€), if you are going to be there 3 days and one of those days isn't Monday (many sites closed). It includes admission to your first two sites such as the Colosseum/Forum/Palantine (9€ - counts as 1 admission) and the Borghese (9.5€). The pass will let you by pass the ticket lines (you usually head to the group/tour entrance). The Borghese requires a reservation which you can make by e-mailing and telling them you will be using your pass. You also get discounts to other websites for the 3 days and a 3 day transportation pass.
www.romapass.it

For the Vatican, you can book tours or just tickets on their website. This will also let you bypass ticket lines.
http://mv.vatican.va/3_EN/pages/MV_Home.html

You can make reservations for museums in Florence on their website (covers all state museums in Florence).
http://www.uffizi.firenze.it/english/Default.asp?

For Sorrento, if you are planning quite a bit of sightseeing, you might want to get one of the Campania Arte Cards. Possibly the 3 day Tutta la Regione which includes transportation for the entire region (trains/trams/buses - from Naples all the way to Paestum if you want) and admission to two sites. In the past the transport also included a one way ticket (Naples/Sorrento I think) on the Metro del Mare, but I don't see that listed on the website. You could e-mail and ask if that was still part of the pass.

http://www.artecard.it/EN/Home.cfm

http://www.metrodelmare.com/

kybourbon, great info.

anything for venice that would behoove getting a pass in advance?

All are on Venice Connected and cheaper if you book in advance than paying at the door. I don't usually go to Venice.
http://www.veniceconnected.com/

Thanks for the great information. This is very helpful! Is Sorrento a good choice to use as a home base for day trips to the Amalfi Coast? What about a day trip to Capri or Anacapri from there?

In Venice I'd advise booking for St Mark's if you want to go inside the basilica, otherwise the queues are very long. If you want to go on the 'Secret Itineraries' tour of the Doge's Palace then book that. Otherwise you don't need to book for normal entry to the Doge's Palace or for the Accademia, IME, if you get there soon after opening time. If you want to visit Wagner's apartment you need to book.