Got back from my second trip to Madrid earlier this month (just passing through on my way to and from La Coruña) and once again found the
Hostal Barrera to be a great place to stay.
It is on C/Atocha, 96, up the street from Atocha Station, near the Reina Sofia and the Prado, a block from the Anton Martin Metro station, nearby Santa Ana/Huertas, and in easy walking distance to the Plaza Mayor and central Madrid.
My traveling companions and I stayed in two superior double rooms for 56 € but standard doubles are 50 € and a single is 35 €. Both rooms were comfortable, tastefully decorated, immaculate, and quiet thanks to the double-glazed windows. All rooms have telephones, televisions, air conditioning, and in-suite bathrooms (with welcome high pressure and hot water).
Nieves and her staff, who are at the desk 24 hours a day, were unfailingly friendly and helpful.