Geografica Oleicola
This is a very useful service if you know the province, municipality, polygono and parcela of the land you are looking for. Generally excellent maps and aerial photos.
Click here for Geografica Oleicola. (only works on Windows and Internet Explorer browsers).
The Oficina Virtual del Catastro is another useful service for finding properties registered in Spain. Also you can calculate the taxable value of a property by going here.
Michelin Maps are good for locations and directions.