Toastmasters is a non-profit educational organization that teaches public speaking and leadership skills through a network of meeting locations. They have several chapters in the Los Angeles area which you can find via their website, which also has a variety of useful free resources for public speaking.
Looking for inspiration for your next speech or want to see how the pros do it? Check out some TED Talks! They're brief presentations usually under 18 minutes given by today's most fascinating thinkers and doers.
The Dictionary of Debate and Public Speaking contains over 600 terms and concepts associated with debate and public speaking. Designed for debaters, coaches, and judges, its scope is international, and it includes terms from a wide variety of debate formats. The emphasis is practical; entries provide the user not only a detailed definition of each term but also examples of how the term would be used in debate. Definitions are nuanced so that the user can distinguish how the term is defined and used in a variety of formats.