Dizionario Collins: Among the best online dictionaries; quite user-friendly
Dizionari e glossari: retorica, stilistica, metrica, ecc.
ForeignWord.com: Rather good and user-friendly
The Logos Dictionary: An amazing resource. Much, much more than a dictionary!
Girodivite.it: A dictionary of writers, scriptwriters, directors, and actors who have contributed to the development of world cinema.