Diccionario de uso del español María Moliner is one of the most prestigious and reliable dictionaries in the market. It was first released in 1966 by the Spanish librarian and lexicographe María Moliner, and has been updated several times since then.
Diccionario panhispánico de dudas is a Spanish dictionary that provides recommendations on how to use Spanish vocabulary correctly. It's a very useful dictionary for those who want to proofread and correct documents in Spanish.
Diccionario Básico RAE is a dictionary edited by the Real Academia de la Lengua Española and specially developed for kids in elementary school. It provides the key tools for teachers to help students develop their language skills and discover the world of words.