Aria Database (http://www.aria-database.com/)
The Aria Database is a diverse collection of information on over 1000 operatic arias. Designed for singers and non-singers alike, the database includes translations and aria texts of most arias as well as a collection of MIDI files of operatic arias and ensembles.

ACDA (https://acda.org/)
American Choral Director's Association

Choral Net (http://www.choralnet.org/)
The Internet Center for Choral Music

Chorus America (http://www.chorusamerica.org/)
Chorus America is the national service organization that promotes the highest artistic quality, development and growth of vocal ensembles, advocates the fair remuneration of professional singers and choruses that provide professional services, and stimulates greater understanding, appreciation, and enjoyment of choral music throughout North America.

Choral Public Domain Library  (https://www.cpdl.org/wiki/)

Dalcroze Society of America (https://dalcrozeusa.org/)

NAfME: The National Association for Music Education (https://nafme.org/)
VCDA/VMEA is an affiliated unit of MENC. Membership in NAfME is required to be a VCDA/VMEA member.

Organization of American Kodaly Educators (https://www.oake.org/)

The lied and song text page (https://www.lieder.net/)
An Archive of Texts to Lieder (Art Songs) and Other Classical Vocal Pieces

The National Association of Teachers of Singing, Inc. (http://www.nats.org/)
NATS is a nonprofit organization dedicated to encouraging the highest standards of singing through excellence in teaching and the promotion of vocal education and research. Our goals include the professional advancement of the talented and the enrichment of the general public. With over 5,000 members in the United States, Canada, and more than 25 other countries, we are the largest association of teachers of singing in the world. 

Texas Literature Manual (https://www.uiltexas.org/pml/)