My husband is Thai and he tells me this is the most authentic Thai restaurant (even better than ones in Thai Town) in the LA/OC area. The cuisine specializes in dishes from Northern Thailand (where his family is from). There was a fire at the Garden Grove location, but they are open at 11951 Beach Blvd. in Stanton (phone 714-799-2031).
We always order many of the same dishes when we go there: BBQ chicken, tod mun (fish cakes... these are my favorite!), sausage (everyone's favorite!!!), steak, beef panang (a red curry), ong choi (I can't spell the Thai word for it), and what we call "crab cakes", but they're really crab and pork dumplings. There's lots of other great dishes... and don't forget the sticky rice and mango for dessert!
If you want authentic Thai food (and you're more adventurous than pad thai) you can't go wrong at Thai Nakorn...
Note that the Mission Viejo location has a new owner and I can no longer vouch for the food there. The GG store will reopen, but I don't know when.
Pros: Fantastic food at a great price
Cons: That there aren't more locations near me!