Angel Tours Rome
Private guided tours at competitive rates.
http://www.angeltoursrome.com/

Appian Line
A tour company with trips nationwide.
http://www.appianline.it/

ArchitecTour
Personalized tours of the Eternal City in the company of a Roman architectural historian.
http://www.architectour.com/

Artu
Artu is an association of certified tour guides.
http://www.arturoma.com/

Avventure Bellissime
Specializes in guided walking tours of Rome, as well as private tours.
http://www.tours-italy.com/

Dorling Kindersley
Download a free audio tour guide to the city courtesy of DK.
http://traveldk.com/about/podcasts

eGuide.it
Search online for an authorized tour guide.
http://www.eguide.it/

Enjoy Rome
Bus and walking tours of Rome.
http://www.enjoyrome.com/main.html

Free Rome
Explore Rome in an electric or micro car.
http://www.freerome.it/

Guided Tour of Rome
Let Carla Viti guide you around her city.
http://www.rome-tour.com/

In Italy.com
In Italy offers private guided tours of the Vatican.
http://www.initaly.com/regions/artists/vatican.htm

Let's Go
Basic information about companies offering organized tours of the city.
http://www.letsgo.com/ROMA/14-ServiceDirectory-249

Manieri del Lazio
Specializes in t ours of medieval castles and villages in the Lazio region.
http://www.manieri.it/

Nerone
Choose from a number of themed tours.
http://www.nerone.cc/

Personal Shopper Agency
Personal shopper service.
http://www.personalshopperagency.com/

Ristotram
Enjoy a meal while touring Rome onboard a tram!
http://www.romeguide.it/FILES/ristoranti/ristotram/ristotram_eng.htm

Roman Homes
Lists a handful of companies in Rome offering walking tours.
http://www.romanhomes.com/your_roman_vacation/walking.htm

Roman Odyssey
Guided tours of the city's architectural and artistic treasures.
http://www.romanodyssey.com/

Romaround
Hire your own licensed English-speaking tour guide.
http://www.romaround.it/

Rome Made to Measure
Customized tours of the Eternal City.
http://www.nerone.cc/romemtm/

Rome Walks
Walking tours of Rome with English-speaking guides.
http://www.romewalks.com/

Select Italy
Runs private guided and walking tours and excursions nationwide.
http://selectitaly.com/

Simply Rome
Links to firms and individuals offering various different guided tours of Rome.
http://www.simplygoingaround.com/show_links.php?category=EXC&city_code=ROM

The Dark Heart of Rome
Runs an "Angels and Demons Tour" of the city, which is based on the famous novel of the same name by Dan Brown.
http://www.thedarkheartofrome.com/
http://www.angelsanddemons.it/

The Eternal Tourist
Web page of an American art historian who offers guided tours of Rome.
http://www.eternaltourist.com/

wGuides.com
Jump on the ATAC number 110 bus for a tour of the city.
http://wguides.com/city/10/69_151241.cfm