When we were at our rural tourism in the Galician countryside, they had a table of books and pamplets. One of them was a very complete guide to rural tourism throughout Spain.

When we got home, I discovered that they had a matching website.

The bad news is that it is in Spanish only. The good news is that even without the language, you will still be able to search the site for ideas.

Once you click on the region you are interested in you will be given three search choices:

Todos (means all listings)
Casa Completa (means rentals with your own kitchens)
Habitaciones (means a room in either a B&B, small inn, or hotel.)

Have fun! http://www.casas-turismo-rural.com

I have a slightly better suggestion. The following web site is the unofficial website for casa rurals in Spain.
www.toprural.com
This web site covers all of Spain and Portugal, plus is presently expanding into 5 other European countries. Although the main language is Spanish it has some adequate information 7 other languages. Only the reviews of the guests have not been changed from the language it was posted in.
All owners have to pay to enter the site, but the site does award “recommended” this means the establishment has got good reviews.

Thanks for the additional recommended site. It never hurts to cross-check sources. So, more than one site is great.

We know of more, but seeing this one has reviews we think it so of some help you make a better choice.
We look forward to hearing from other posters about what they have found useful on the web.