Taxis in Rome - Costly? Reliable?

There's a long line of taxis in front of Termini. The cost of that ride should be under 15 Euros, I would estimate. We've never had a problem with Roman taxis, but then I speak a good bit of Italian. Make sure the guy starts the meter when you get in. Expect to pay a slight surcharge above the total, maybe 1-2 euros. No tip necessary, but you might round up to the next euro. Pay in cash.

The official taxi fares for Rome are below (scroll down for English). I've been ripped off by taxi drivers in NYC and, especially, Washington DC, but never in Rome.
http://www.6645.eu/tariffario-taxi-roma-aggiornato.pdf
To calculate your cost you can use the website below:
http://www.costotaxi.com/?q=it/content/it/taxi-calcolo-della-tariffa-roma
Your departure point is: PIAZZA DEI CINQUECENTO, which is the taxi stand at the Termini station.
The cost for the distance described is probably around €15 euro (a bit more if night or weekends). There is a €1 charge for each piece of luggage (over the first one, which is free).
There is a long queue of taxis on Piazza dei Cinquecento. Getting a taxi at a taxi stand in Rome is just as easy as in any other place.
I'm wondering however where your B&B is. 5.6km from Termini, seems quite a distance for a Centro location. What is the exact address? I hope you didn't get a place far from the city center.

Great, thanks for all the info, Michael and Roberto.

Roberto, we are staying in the Prati district. We wanted to be a bit off the beaten path.

We have never had a bad experience with official Rome taxis. There are relatively inexpensive. There are dozen if not closer to a hundred cabs at Termini. Just be sure to use the official stater and not get grabbed by someone who asks if you need a cab.

What Frank said! Just stand in line and wait your turn. Anyone who pulls you from the line will fleece you.

Once you have your bearings you will find Prati well connected by public transportation and also, depending on your exact location, within walking distance of Piazza Navona.

IMPORTANT. At Termini, there are rogue taxis outside the station on the left. Don't go near them. Continue to walk straight to the front of the station and to the official taxi stand. I've never had a problem there, or by hailing a taxi on the street in Rome - just the rogues at Termini

Very good warnings. Those "rogue" taxi drivers can be pretty aggressive to get customers, even to the point of trying to "help you" with your bags. Just say "No!" very firmly and keep walking.

Last May we arrived in Rome via train at Termini station and got a cab out front to take us to Piazza Navona area. We thought it was legit as he was in a line with other taxis. When we arrived at out hotel he wanted 25 euros plus 10 more for the luggage. We refused to pay the extra and threatened to call the police. He called us many names got in his cab and left. We will be much more careful the next time.

I always Google for the cost of a taxi from the station to my lodging before I enter my destination city. Websites show distance cost for one person, some websites show costs for luggage, and may figure in time of day. I look at several different websites to get the best idea possible, and then round up with extra for the driver.

You can ask your hotel how much the taxi should be as well. And then communicate that number with the driver before you get in. I have taken a lot of taxis in Rome and I only had one try to swindle me (and it was my fault. I was a new traveler and didn't realize I was getting into an unmarked taxi). In general I think the taxi drivers are honest. Also, I haven't been to Italy in about 4 years but it was normal for cab drivers to add a Euro for each big piece of luggage. And there is a night surcharge, about 5 Euro, if you take a cab after 10 pm. Someone please correct me if I am out of date. But I only point this out because sometimes people think they are getting cheated when they really aren't.

Thanks for all the great advice and tips, everyone! Much appreciated!