I usually really love the EyeWitness books, but a few of the ones in Italy were not quite as good as they could be. If you love the EyeWitness series, I would try getting 2 and seeing which one works best.
For a specific guide for Rome, you might want to try a small, compact book that can easily fit in your pocket - "The Rough Guide to Rome (English). You can expect to pay less than $20 for that. It contains maps of the place, and comprehensively explains various areas of Rome.
Another fine reading material to bring with you anywhere would be "The Traveler's Tool Kit." This has many helpful suggestions in traveling that you will find most convenient.
And there is another one that I just learned about for another country you've mentioned. It's "The People's Guide to Mexico." Also a comprehensive guide.
I highly recommend going to your local bookstore and takiing a look at all of the Italy travel guides for sale. Travel guides vary pretty widely, so it's very difficult to recommend one over the other without knowing how a person travels. Some books are geared for budget travelers, some have great color photos, some have very thorough sections on the history of the region, some have comprehensive sections on dining and lodging, some give cursory nods to them, etc. My favorite travel books are published by Lonely Planet, but Moon, Fodor's, Frommer's and Eyewitness are also very good. Going to the bookstore will certainly whet your appetite for your trip and you'll be so excited that you'll probably end up buying more than one guide. Have fun!
Thanks thepiraha, I have been looking at different travel guides at the book store. I just wanted the opinions of some of our well traveled posters here. I bought all sorts of guides for places I've been in the past and they are not all equal.