Operabase: This site is quite comprehensive, providing valuable information on the major opera houses and festivals. One can also view a history of opera. There are also hundreds of links to additional opera resources on the Web.
Opera Glass: At this site one “can get detailed information, including performance histories, synopses, libretti, discographies, pictures, and more.”
“An opera begins long before the curtain goes up and ends long after it has come down. It starts in my imagination, it becomes my life, and it stays part of my life long after I’ve left the opera house.” –Marie Callas