I can thoroughly recommend Mamiani hotel.
We stayed there for a week-end in Rome in January.
We booked a triple room and have been very pleased with the experience. Location is good, within walking distance of the railways, and even closer to a metro station. The room we had was very clean. The decor was basic but we did not expect much for this price. There was TV with satellite channels (all in italian), air-con, hair drier, mini bar, safe and en suite shower/toilette.
They accept credit cards, and it's better to book through one of tripadvisor's recommended website than direct, 70 Euros vs 110 Euros.
The staff at the door was very friendly, even though their english is not very good. On the downside, the hotel is not very visible from the street, you have to know the exact adress to find it. An other negative point is that the walls are quite thin and you can clearly hear the party goers coming back to the hotel in the early morning.
I would definitely stay there again.