About.com: Opera 
Guide featuring links to selected sites.
http://classicalmusic.about.com/od/opera/Operabase
News and reviews, performers and artists, opera houses, recordings and web resources, plus booking details, interactive maps, search tools and timelines. [Dutch, English, French, German, Italian, Portuguese, Spanish]
http://operabase.com/en/
All About Opera
Features information in a searchable database about composers and operas, and includes related news headlines.
http://www.allaboutopera.com/
Opera Basic Dictionary
Devoted fan Mario Biondi has compiled lists of more than 1,500 operas by more than 500 composers, with their countries and dates, as well as thousands of performers and recordings. Searchable by title, composer, and performer. [English and Italian]
http://www.mariobiondi.net/opere/diz_opera_.html
