Having just stayed in several 3 and 4 star hotels whilst following the Vuelta cycling race over the past few weeks. I'm quite annoyed at the charges some hotels make for internet access. eg NH hotels cheapest charge is 10 euros for 1 hours access in a 24 hour period. - No. I didn't use it!!
So how about starting a list of Hostels and Hotels that offer free wifi?

I'll start you off.
Madrid: Hostal Chelo in Calle Hortaleza

You're asking about only Madrid or all of Spain?

I think nearly all hotels in Spain charge for internet access. It really is a disgrace if you ask me. It costs them so little although they would have to put up routers on each floor and, probably, both ends of the floor too. But their monthly cost is little and they overcharge for this.

In Madrid, Hostal Adriano has free WiFi.

Saludos, MadridMan

Madrid: Hostal Martin & sister hostel Hostal Cervelo , both on Calle de Atocha near Plaza Jacinto Benavente.

Madrid: Hostal Villagarcia on Calle Fuencarral very near Gran Via also has free WiFi.

Madrid: Hostal Madrid (a.k.a. "Hospedaje Madrid") has free WiFi in the hostel rooms and its apartments.

Madrid: Hostal La Plata on Gran Via has Wi-Fi but their website doesn't say if it's free - but I imagine it is.

Saludos, MadridMan

Madrid: Hostal Josefina on Gran Via/Callao has free Wi-Fi.

Saludos, MadridMan

Madrid: Hostal Dominguez near Chueca has free WiFi too!

Jan D, you were you asking about hostels and hotels in ALL of Spain or just Madrid? Me know soon before I complete the country one at a time. Thanks!

Madrid: Hostal Bruña has free Wi-Fi at the reception area.

Ha Ha !!
Seems it might be better to have a list of hotels that charge silly prices for Wifi rather than those that charge nothing!!