I think the champagne truffles at Teuscher, in Beverly Hills, while obscenely expensive, are phenomenally good. Oddly, I've never been bowled over by anything else there, but the champagne truffles are awesome.
I also really like Leonidas on Larchmont. Somewhat more modestly priced than Teuscher, and excellent, interesting flavors.
Lastly, if you're not married to buying locally, mail order from L.A. Burdick in New Hampshire is wonderful. Some of the best chocolate around, in my view. Website is here: http://www.burdickchocolate.com/ .
Teuscher chocolates & caf
9548 Brighton Way, Beverly Hills, CA
Leonidas Belgian Chocolat
201 N Larchmont Blvd, Los Angeles, CA