Roma Pass

Generally speaking the Roma Pass is worth it if you plan to see the 2 free sites (i.e., Colosseum + Borghese Gallery) or use any public transportation. I don't remember the exact amounts, but the Colosseum/Forum/Palentine (all one ticket) costs 13 or 14 euro, the Borghese costs maybe 8 or 9. Even if you only used public transportation to get to Ostia Antica, that'd be 2 euro. The Roma Pass costs 23 euro. You can see that at this point it makes sense to buy the pass.

Another factor to consider is convenience. The Roma Pass is a great way to bypass the line to buy tickets at the Colosseum. It's also nice not to have to deal with a bunch of individual tickets/change, and being able to just slide your transportation pass through the metro and ride all over town is much nicer than trying to figure out a kiosk in Italian as your train is pulling up to the platform.

Ostia Antica is one of the free sights you can use your Roma Pass for. However, it is less expensive than the Borghese Gallery and some of the museums, so plan accordingly. (I think you get 2 sites free and then after that you get a discount.) We used the pass for Ostia Antica and The Collosseum and then used the 3 day transit pass multiple times. We saved about $7 and some time (since you don't have to wait in line at the Colosseum, just go through security and you are in) It really comes down to how much you plan on using buses or the metro.

Before you decide to buy the Roma Pass, read Ron's blog on this very subject. He just posted a very thoughtful article dealing with the Roma Pass. Here is the link:

http://www.roninrome.com/2009/04/27/should-i-buy-a-roma-pass/

The way the roma pass works is that you use your two top most expensive entires first, the Borghese Gallery being at the top and the Colosseum being next. Then it pays for it self after that in many ways and at any thing else you see in the next two days. We used it, as much as we could with the city bus and the subways, so it saved us about 60 euros.