I'm officially a converted fan of Erawan Thai Restaurant. Before then, i've heard so much about it from friends, and further that eiling's- and so i finally visit the restaurant, subsequently went back again a week later. (because it was THAT good)
If it's even possible, the brothers operating Erawan again and again impress me with their authentic thai dishes, and i've tried quite a bit and none of them has actually failed me.
Erawan is located at Dataran Sunway, close proximity of Starbucks coffee. It's quite easily missed as it only operates one shop lots, and at most times it is impossibly packed. Strongly advise to make reservation beforehand to avoid any dissapointment- and if you are familiar you should also pre-order your dishes prior visits. You can refer to their menu (and prices) here.
Service was actually REALLY slow during dinner time when it was jam packed with diners. This is mainly reason to orders being taken by only one person, also the co-owner of the restaurant, Anan.
That aside, Anan is actually a friendly guy, on my subsequent visit during lunch when things are slightly slow, he actually had time to chitchat with us, show us some of his restaurant reviews and service has also improved somewhat.
So if you are willing to be patient (for like half an hour to get your order in), then you have no reason not to go. Otherwise, do consider going during less peak hours.