You are looking for non-spanish books in Madrid and are not satisfied by El Corte Ingles or the FNAC? Well, why not have a look at the following bookstores?
TURNER: Principe de Vergara 206 (Metro Concha Espina, Mond.-fri. 10:00-20:00, saturday 10:00-14:00).
On the other side of the street, in some fjord, there is also a german bookstore. I ought to find its adress.
Booksellers: Jose Abascal 48 (Metro Gregorio Marannon, Mond.-Fri. 9:30-14:00, 17:00-20:00, saturday 10:00-14:00).
El Corte Ingles or in the local FNAC (Especially if you're looking for french books).
There is an italian bookstore near the italian embassy....
DUTCH: Het Boekenweb, BRUNA, Het Boeknet, Querido.
AFRIKAANS: Die Boekenet.
DEUTSCH: ROWOHLT, D.T.V., Suhrkamp, BUCH, Amazon.de.
ENGLISH: Internet Bookshop, PENGUIN, AMAZON.COM.
Dutch: Volkskrant, De Limburger, Het NRC Handelsblad, De Telegraaf.
Spanish: El Pais, El Mundo, ABC, MARCA.
Other European: Die Zeit (D), La Stampa (I).
Peruvian: La Republica, El Comercio, Caretas.
U.S.A.: The Nieuw Amsterdam Times, Miami Herald.