The section devoted to Spanish is growing quite slowly, however, this new link proves to be really useful.
It is a link from the University of Oviedo and it contains a Spanish dictionary, Dictionary of synonyms, antonyms,links to other dictionaries, including some English ones, as well as a great "conjugator": you can introduce any verb in Spanish and they give you all the tenses....
Really worth visiting..remember, it is included in the section devoted to Links related to Spanish under the name Universidad de Oviedo: Dictionaries and verb tenses