I've been told that the best one now is one by Zimmerman, Svensson and another one by editorial OMEGA.
The one I've got is Peterson's guide which has the problem that the picture and the maps of distribution areas and seasons are not at the same pages.
I think there was another one good by Johnsson or something like that, I don't remember.
Usually, the guides cover all Europe, so maybe you can find someone good in English or French. As you see, most of the autors of the guides are not Spanish, so they must be in other languages. If you prefer the name of the birds in Spanish, then you will find them in any book shop here.

Thank you very much Miguelito! I'll look up these names, but will buy a bird book in Spanish for my trip, as I've just finished a Spanish course, and intend on speaking and reading it as much as possible.

plumepoppy (nice name by the way ),

here is a link to bird watching in Tarifa and the local ornithological society there. u can also whale watch and the beaches are fantastic.
the center of the old town is precious as well!

ornithological society Cigüeña Negra

Thank you Guapetona! That information is worth gold ... oooops, should I say feathers. I have a theory, for having seen so many storks on monastery towers in Spain, that storks were bell-ringing monks in a previous life, and that they have come back as their guardians.

Why thank you for the compliment. A plumepoppy is a flower, and of course, plume means feather ... follow my drift ...

Plumepoppy,
Hope you have a wonderful trip. When we visited Salamanca we saw Albatrosses and their nests in the tower of the University. I took photos.

Aaaaaah ma chère Booklady, when I arrive in Salamanca and see my first albatrosses, I will wish them a salud cordial de la Dona de los libros (sorry, you'll have the visualize the accents...).