Casting Call Listings

Actor's Access - vast majority of casting calls for speaking roles come through here
LA Casting
Casting Frontier
Backstage
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
Commercial Casting Directors Association
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/Permits

CRBC - productions shooting currently in BC Canada
FilmLA - Filming permits in Los Angeles

Music Industry Links

ASCAP - ASCAP Repertory - song searches
BMI - BMI Repertoire - song searches
SESAC - SESAC Repertory - song searches
American Federation of Musicians