Young,
I am very familiar with every BMW dealer in the LA County area and then some.
Without a doubt, the best dealer in terms of sales support, courtesy, honesty, etc. etc. is STEVE THOMAS BMW in Camarillo. Yes, it's Ventura County, but they are really, really nice guys.
I would recommend Tony Rossi-- he is a great salesman. Not only do they have an impressive roster of celebrity clients, but pricing wise they are aggressive and fair. For instance, they have a strict policy of NEVER charging over MSRP on a car, for Mr. Thomas believes that this is the worst thing you can do to customers.
They also have a big initiative to never be undersold. They want to beat any deal in town! It's the first time I have ever heard of such a thing from a Bimmer dealer...
I have the regret of not buying my BMW there before, but I can assure that my next purchase will be with them.
PM me and I can give you more details, perhaps even meet your friend down there to make the introduction, since they are right over the hill from me
As far as SERVICE/MAINTENANCE is concerned, I would recommend Century West BMW near Universal Studios. My uncle is one of the top techs there and he always hooks all my friends up! He is the ONLY one who ever touches my cars...
Hope this helps.