Operabase -- http://www.operabase.com/en/
The Aria Database -- http://www.aria-database.com/index2.html
Kirchenmusik online -- http://home.t-online.de/home/jo_vo/homepage.htm
Musica classica-Classical music -- http://www.karadar.net/Default.htm
Texts of art songs etc. -- http://www.recmusic.org/lieder/, http://www.recmusic.org/siteindex.html
Lieder of specific composers -- http://www.gopera.com/lieder/
Classical music and more -- http://www.iclassics.com/iclassics/homepage.jsp
Classical composers -- http://www.classical-composers.org/
Classical Music Lovers' exchange -- http://cmle.com/
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The Metropolitan Opera -- http://metopera.org/
Carnegie Hall -- http://www.carnegiehall.org/TextSite/main.html