Bangkok 4 is my favorite Thai restaurant.  It's in the South Coast Plaza Crystal Court behind South Coast Plaza.  It's on the 3rd floor.

I'm not sure if this is real Thai food or upscale Californiaized Thai food but I think is delicious.  It's a little expensive.  The kind of place you'd go on a relatively nice dinner with your girlfriend.  If you just want to pig out go to the Thai BBQ next to Tommy Sushi.