Full text articles from scholarly journals in the arts, humanities, sciences, and social sciences.
An online language-learning system teaching actual conversation skills for a wide variety of languages.
Real Academia Española (Free online Diccionario of the Royal Spanish Academy, in Madrid)
As authoritative in the Hispanophone world as the OED is, for English speakers. Offers detailed glosses of searched words, including information on regional dialects, different registers of usage, etymologies, and all possible alternate meanings. The interface, including glosses, is in Spanish.