I discovered quite by accident two tips which served us well on this last trip to Rome, and saved us money.
The first is to search the iTunes store and the web for free audioguide downloads for the sights that we were going to see. Not all audioguides are created equal, and there is the disadvantage that they don’t corrispond to the numbers posted on the site, and they don’t come with a map (usually) but, they are often given by tour guides who do give tours at that location, and they are often more brief and give more interesting and relevant information. Also, sometimes free audioguides cover places that don’t have official ones. We found free audioguides for the Colloseum, Roman Forum, Circus Maximus, Fountain of Trevi, and the Pantheon.
The second is, in places where we couldn’t find a free audioguide, we realized that many of had a place to plug in headphones and we had purchased a stereo splitter for us to listen to my ipod together. So we did the same thing, plug in splitter and two sets of headphones and have two people listen to one audioguide. For some sites, it probably helped that we have noise-isolating headphones, otherwise it might hav ebeen difficult to hear. One implication of all of this is that you have to stick close together. This isn’t a problem for us as we like being able to discuss what is talked about, so we found it a good thing to be listening to the same thing at the same time.