The Roma pass is well worth the 25 euro investment. Directly from their web site
http://www.romapass.it/p.aspx?t=columns&c=2&l=en&tid=2 , here is an overview:
Price per unit: € 25,00
Roma Pass, which is sponsored by Rome City Council and the Ministry for the Arts and Cultural activities, in collaboration with ATAC, the public transport company, is the capital's special tourist-cultural card that enables both tourists and interested local residents, the opportunity to benefit from various discounts and services that make it easier and cheaper to enjoy the splendours of Rome.
Free entry to the first 2 visited museums and / or archaeological sites of your choice
Reduced ticket prices to all other museums and / or archaeological sites visited thereafter
Free use of the city's public transport network (urban buses and trains, Underground lines A and B, Met.Ro trains: Roma - Lido, Roma - Viterbo for the Roma - Sacrofano section, Roma - Pantano railways lines within the urban territory of the City of Rome) Trenitalia trains and Cotral buses are not included.
Discounted tickets to exhibitions, events and other collaborating operators and businesses.
Reduced charges for use of the On-call Multi-lingual Medical Service for Tourists (MET Travel Health)
Tourist cultural service Roma Informa.
At the Colosseum a reserved turnstile is available for Roma Pass holders to get direct access to the monument
In the kit::
The Roma Pass card: the card used to visit museums / archaeological sites and on the public transport system as described above.
Roma MAP: A map featuring all the Tourist Information Points, Metro stations, museums and other sites of interest (complete with addresses, tel. no?s opening times and nearest bus stops and metro stations);
Roma Pass Guide: The guide to all participating museums and sites;
Roma News: a programme detailing all the events and services for tourists offering discounts, divided by type: art, dance, music, theatre, reviews, exhibitions, panoramic tours, as well as tourist services at the Lido in Ostia and MET Travel Health
Roma Informa: the card that provides details of how to access information on events and other useful services via internet