for truly life-transforming Chinese in LA, hop in your car and drive out to San Gabriel/ Monterey Park, the 'Beverly Hills' of the expat set. There are incredible restaurants out there. If you have time for Dim Sum you have to try Ocean Star, which has been consistently amazing for years and a local favorite. Maybe the best I have had in the US - and I'm a huge dim sum fan/eater thanks to growing up in a city with great Dim Sum. It is worth every minute of the drive.
Ocean Star
145 N Atlantic Blvd
Monterey Park, CA 91754-1581
(626) 308-2128
But that's just the beginning.
Here's a citysearch guide to Monterey Park, which is chock full of amazing Chinese goodness from various regions. I recommend driving around and checking out as many places as you can. There are some fantastic Chinese supermarkets out there too - just as nice as any you might find in Hong Kong or Taiwan. After living out there, I found Chinese Markets in other US cities to be quite dark, smelly, and depressing by comparison.
CONNOISSEUR, n. A specialist who knows everything about something and nothing about anything else.
-Ambrose Bierce, The Devil's Dictionary
www.cakeandcommerce.com