Don't know about the "Top 3." I guess that would depend on who you talk to. Here are some heavy hittters:
Sara Finn, Randi Hiller
588 N Larchmont, 1st Fl Los Angeles CA 90004
Credits: Iron Man, Crash, George W, just to name a fewFrancine Maisler
Francine Maisler Casting
10202 W Washington Blvd, Jimmy Stewart Bldg, #207
Culver City CA 90232
Credits: Tropic Thunder, A Knights Tale, MilkAllison Jones
Allison Jones Casting
1438 N Gower St, Mailbox 3 Los Angeles CA 90028
Known for finding great comics for films/television.
There are so many more. You can't just nail it down to the "top 3," because there so many of them that have a part in casting major films. No phone numbers, sorry. You can probably search their numbers online, or you may have get a directory book. They are sold all over. You can probably even call directory assistance and get the numbers. The web is full or resources for actors.
Some other noteworthy names, in which I have no contact info:
Robert J. Ulrich, Eric Dawson, and Carol Kritzer CSI, Saving Grace
April Webster: Lost
Juliet Taylor, Sleepless in Seattle, Schindler's List, Taxi Driver
I know you mentioned film casting, however the dynamic of television has changed through the years. That is why you see so many movie stars move to TV. It often holds more prestige. Also, I know you mentioned LA, but the East Coast has some pretty big names as well, regarding casting directors.
Edited by Hugh on 10/9/2009 at 12:35 PM EST