same question as Milan.

We're looking for a budget hotel, outside of Rome proper, on a train line for quick runs into the city. Thank you!

What is your budget? Surely there is a small hotel or hostel in each city that would be a better choice that staying on the outskirts.

except we'll have a car, so we figure it will be less of a hassle to stay outside the city

We stayed at the Meditteraneo (spell ??) right next to the train station on Via Cavour - what a gem and the staff was the best - even went back the next year!! and will go back again. I thought the prices were very reasonable compared to other hotels.

Try Ostia - there is a train that takes you into Rome and there you can change to pick-up the metro to get to other parts of the city. Can't offer any names of hotels but that is what my parents did when they had a rental car.

We stayed in the City Guest House in Rome on one of our trips there. We bought it as a package deal that included the airfare. The hotel itself isn't bad. Its in Rome, but in a residential area away from the center, in an area called Tuscolana. Its near the end of the Line A metro, and its a close five minute walk away. http://www.cityguesthouse.com/accommodation.html

You may also want to consider something in Bracciano, on lake Bracciano. You can take a commuter train to Rome. The town is quite interesting and there is a neat castle that one can tour.
http://www.lakebracciano.com/lakebra.../paesi_en.html

Tracy