Alfanet
Search the bus or street you need using this tool.
http://www.alfanet.it/Mappadiroma/default.html

ATAC
Online journey planner: map your route; check timetables; find out more about fares; and consult maps.
http://www.atac.roma.it/

Bed & Breakfast Roma
Download Rome bus line, night bus, metro, train and tram maps at this site.
http://www.bedroma.com/mappe/map_consulta.asp

BUG
Useful overview of public transport in the city.
http://www.bugeurope.com/rome/ga.html

COTRAL
Check the company's bus timetables.
http://www.cotralspa.it:8115/standard/index_en.htm

COTRAL
Cotral is the main operator of buses in Rome and the surrounding region. Alas, the website is largely in Italian.
http://www.cotralspa.it/

Enjoy Rome
The site contains a particularly useful section on Rome's bus service with information on night buses, useful routes, electric buses, "J" buses and fares.
http://www.enjoyrome.com/tourist/cityguide/public.transportation.html

My Travel Guide
Useful tram routes outlined.
http://www.mytravelguide.com/city-guide/Europe-&-Russia/Italy/Rome/Useful-tram-routes

No Place Like Rome
Details the telephone numbers of Rome's main train stations.
http://www.noplacelikerome.com/driving.htm

Roma Termini
Official website of Rome's main train station.
http://www.romatermini.it/

Roman Homes
Tips on using public transport or taking a taxi in Rome.
http://www.romanhomes.com/your_roman_vacation/transport.htm

Rome's Public Transport
Covers everything you need to know about the city's public transport system, from the network to the different types of tickets available.
http://it.geocities.com/mp_pollett/roma-tr.htm

Rome Buddy.com
An introduction to metro and bus passes and tickets.
http://www.romebuddy.com/givesadvice/metropasses.html

Rome Central
Find out more about the different types of tickets available for use on Rome's public transport network.
http://www.romecentral.com/transportation_bus.php