How did you prepare to see these sites in Italy?

There are these flip books that show the Forum as it is now, and you flip over transparent pages to see what it looked like when each building was in use. The difference is astounding. Now it is an evocative relic - - back then it was a bit dull and monolithic, with a utilitarian feel. The flip books also tell about each scene. Those are definitely worth a look (you might be able to get one in advance, but you might have to wait till Rome).

Free audio tours are available on ITunes with maps.
http://itunes.apple.com/us/podcast/italy-audio-tours/id272230438

Pierreci was the official tour booking agent so they should be cheapest on the underground tour.
http://www.pierreci.it/home-page/IT.aspx?DefaultLanguage=IT

Forgot my favorite book.

Not my favorite Rome book. Not my favorite history book. It is my favorite book of all time, period - - this book has taught me more about the nature of the underlying character of human civilization than anything ever, and it also has taught me vastly about social psychology than I ever learned anywhere, and I am a psychologist:
http://www.amazon.com/Day-Life-Ancient-Rome-Curiosities/dp/1933372710

I read "The Fires of Vesuvius: Pompeii Lost and Found" by Mary Beard before visiting Pompeii.

The Rick Steves audio guides/ podcasts are helpful.

The Pantheon is intact--not a pile of stones-- so any guidebook should provide the information you need.

There is a wonderful on-line course (free) that is an actual course at Yale Univ on Houses and Villas of Pompeii. You can watch video of actual lectures, plus there are photos and text you can read. It made a huge difference in my visit to Pompeii. http://academicearth.org/lectures/pompeii-houses-villas-architecture

Also the official site (Pompeii) has their entire (very detailed) brochure on line. Read it ahead of time.

I read everything I can find. My husband might peruse one (and only one) guidebook, usually on the long flight from home. We often rent audio guides and sometimes take a guided tour; I often tell him things I've learned in my readings. I feel pressured to see and understand everything; he's perfectly happy absorbing what he absorbs. He occasionally reminds me it's a vacation and there is no test at the end.

Check out the mysteries set in Ancient Rome by Lindsey Davis. They give a plethora of information about how the average roman lived at the time (a lot kind of surprising given how far most of europe fell back in the dark ages) as well as an interesting view of the political and social scene. And fun mysteries in their own right.

I know I was thinking back to the mysteries when I toured Pompeii, which was much less urban then Rome in some way (no 5 or 6 story apartment houses, more luxury villas) but also explained a lot about the basics of each town (the bakeries, food shops, restaurants etc).

The Yale course referenced by Isabel is excellent, not just for the Pompeii lecture but the entire series. Not only does it give you a much deeper insight into the sites you see throughout Rome and Pompeii, it gives ideas for more sites than you will ever read about in the guide books.

On the Open Yale website, you can get the audio and download it to iTunes, watch the video, and read transcripts of all the lectures: http://oyc.yale.edu/history-art/hsar-252

wow these recommendations are fantastic! I am going to the library tomorrow to pick up a couple of the books! And the Yale courses look right up our alley!

bookmarking

Michelin Green Guides and Cadogan Guides, plus just a lot of reading of good history books. I do not ever do Rick Steves, as I think he's a complete idiot when it comes to history and language, but many people enjoy his approach to Europe. Depends on what you want. But do go to the library and get as much material as you can get your hands on.

The Yale website looks fabulous - thanks for that!

For the Colosseum, the lower priced tour offers an audio guide which is more than adequate. Prepare for the long lines. I just do not think the accompanied, higher priced tours are worth it. Pantheon does not require a tour guide or audio. You will be awestruck just by standing inside! For Pompeii I always recommend Carrani Tours. They pick you up at your Rome hotel early in the AM and you are in Pompeii by 10 am. You will have to suffer through one tourist stop at a furniture or cameo shop, but it is always interesting and relaxing way to visit Pompeii.