Casting Call Listings

Actor's Access - vast majority of casting calls for speaking roles come through here
LA Casting
Casting Frontier
Central Casting - background acting 'extras'

Unions and Guilds

SAG-AFTRA - The Screen Actors Guild
Actor's Equity Association - In the US, for theater actors and more
Casting Society of America - casting directors
Producer's Guild of America
Director's Guild of America
Writer's Guild of America
Associations and Guilds - California
Associations and Guilds - New York
Other unions and guilds - per Wikipedia

Databases of productions

IMDb - Internet Movie Database (tv and film)
IBDB - Internet Broadway Database
about the artists - theater
IAFD - Internet Adult Film Database
Discogs - Discogs Music Database

Production Lists

CRBC - productions shooting currently in BC Canada

Music Industry Links

Trans Chorus of LA
GALA Choruses - association of LGBT choruses worldwide
ASCAP Repertory - song searches
BMI Repertoire - song searches
SESAC Repertory - song searches