E-Libretto 
A collection of more than 200 electronic opera libretti, full text.
http://www.geocities.com/voyerju/libretti.htmlLibretto Homepage
Public domain opera libretti and other vocal texts.
http://opera.stanford.edu/iu/librettim.html
English Opera Translations
English performing translations (librettos) of popular operas, including Marriage of Figaro, La Boheme, Gianni Schicchi, Pagliacci, translated by Ken Jakobs.
http://www.englishoperatranslations.com
OperaGlass: Operas
Extensive directory by opera of libretti, synopses, performance history, background and discography.
http://opera.stanford.edu/operas.html
Karada Classical Music: Opera's Librettos
Biographies of composers and lists of their works. Includes libretti for the works of some of them.
http://www.karadar.it/Operas/
Opernführer / Opera Guide
A collection of opera libretti (originals and translations), with links to similar sites. [German/English]
http://www.opera-guide.ch/
