Useful music links:

http://ingeb.org/home.html
“The Leader in Lieder mit Midi Melodies”
A huge site with thousands of easy to find lyrics. Covering folk songs from 44 countries in many languages. Many songs have mp3 files, midi files or sheet music. 

http://www.contemplator.com/
Contemplator.com
Large database with lyrics and midis of folk music from England, Scotland, Ireland, Wales and American. 

http://www.mysheetmusic.com
Free sheet music. Quality PDF files. No lyrics 

http://www.geocities.com/voyerju/libretti.html
“Opera e-libretto”
Collection of libretti from many different operas 

http://www.aria-database.com/
Enormous database of opera lyrics, some midis and translations 

http://www.tenorissimo.com/domingo/Words/
Popular Italian song lyrics 

http://www.mediaversal.com/wesley/
Various modern songs and a .pdf downloadable songbook.

http://classicrock.about.com/
Lyrics of popular songs (modern and some classical) 

http://www.italianfolkmusic.com/home.html
A good variety of Italian folk songs 

http://www.operaheb.co.il/frames/arias_f.html
and

http://www.operaheb.co.il/frames/libretto_f.html
Lyrics of some opera areas 

http://www.dlib.indiana.edu/variations/scores/
William and Gayle Cook Music Library
Indiana University School of Music. Useful site offering opera lyrics and sheet music 

http://www.recmusic.org/lieder/
"An Archive of Texts to Lieder and other Classical Art Songs (Kunstlieder, Mélodies, Canzoni, Romansy, Canciones, Liederen, Canções, Sånger, Laulua, etc.) as well as many choral works and other types of classical vocal pieces, with thousands of translations to English, French and other languages."

http://muslib.mmv.ru/index_eng.html
The Music Library. A free music library offering free sheetmusic for various instrument the following catagories: Piano, scores, emsambles, choir music, vocal music, songs, guitar, jazz music, flute, recorder, oboe, clarinet, saxophone, trumpet, violin and contrabass. Languages: English, Russian and Japanese. Also some lyrics.

http://www.virtualsheetmusic.com/
Downloadable music scores for piano, violin, trumpet and other instruments.
Both free and for sale items.

http://www.traditionalmusic.co.uk/
The traditional music here is split into 22 different songbooks or tune-books, each dedicated to a particular type of traditional folk or roots music. There are musical scores with chords from which you can print sheet music and lyrics, there are also MIDI files to play so you can hear what the tunes sound like.

http://voiceacting.com/
James Alburger's book, workshops and seminars in "The Art of Voice Acting", the craft and business of performing for voice-over.

http://www.karadar.com 
Karadar Classical Music
Valuable source of Lieder texts, opera librettos, midi recordings and other material.