Here are a few good ones for you:
Nadia Eftedal, Mark & Viola Weiss, Tom Hicks, Tomas & Isabela, Shirley Ballas, Aliona (sorry, don't remember her last name), Mike & Alice Cho.
All of the above mentioned instructors teach either at the Westmor studio in Koreatown, L.A. Dance Experience in Westwood, or Regency Ballroom in Torrance.
There are more, but I don't know everybody's name. Everybody I mentioned are fantastic instructors (most equal to or above the calibre of the Dancing w/ the Stars set). Shirley Ballas is absolutely world class.
If you want to shop around to make sure you make the right decision, take some time out to come down to these studios and watch the lessons, talk to people, and get a feel for what's available. Trust me, there's plenty of good talent here. You can find all the info you need about these studios in our directory.
Regards,
Jonathan Atkinson
www.ballroomdancers.com