Rome has a new tourist discount card - the Roma Pass. This 18€ pass is good for 3 days - it gives you free admission for the first 2 museums you visit, with reduced admission on any others after that, and free public transportation for all 3 days. It also comes with a map and a booklet detailing what museums, sites, etc. are eligible. This is an amazing deal - especially if you are staying in Rome for just a few days.