News:
Operabase
Playbill
Playbill Arts
OperaGlass
Opera News

Reference Resources:

Ithaca College Music Library
Naxos Music Library
Grove Music On-line
The Business of Singing Worldcat.org
Internet Archive (including "Wayback Machine")
Catalogues of composers' works
Karadar Classical Music
The Scenes Database
The Aria Database
Musical Theatre Songs
Library of Congress

Music and Scores:
IMSLP International Music Scores Library
Classical Vocal Reprints Educational Music Services

Scripts, Monologues, and Libretti:
Simply Scripts
Opera-L
Karadar Classical Music
Monologue Archive
Audition Preparation
Musical Theater Audition

Translations:
Babelfish
Rec Music
The Aria Database

Local Opera Companies:
Syracuse Opera
Tri-Cities Opera

Summer and Young Artist Program Information:
YAP Tracker

Professional Affiliations:
Opera America
Musical America
Classical Singer
National Association of Teachers of Singing

Choral Music Resources:
Choral Public Domain Library
Musica International Virtual Choral Library

Early and Sacred Music:
Goldberg Early Music Portal GFHandel.org
Bach Cantatas Website
Early Music FAQ CyberHymnal

Musical Theater:
Playbill
Musical Theatre International
R&H Theatricals
The Guide to Musical Theatre
British Musical Theatre
Stephen Sondheim Reference Guide
Gilbert & Sullivan Archive
Musical Theater Audition
Musicals101
Backstage