Longrain is the most delicious Thai food you will ever have ... no bookings though, so unless you want to wait for a couple of hours in the bar for a table (which frankly is not the worst outcome), get there around 6pm. Their cocktails have to be tried to be believed. Milsons in Kirribilli has wonderful modern Australian food and an elegant atmosphere-fantastic for a special occasion.
85 Commonwealth St., Sydney 2010, Australia, Phone: 02-9280-2888
www.longrain.com.au/
Google map: tinyurl.com/yaqaool
Updates
Best Thai food I have ever had and pretty cheap when you consider a main course is big enough for two and really great cocktails - just don't be fooled into thinking the Melbourne version is anything close to this. No atmosphere, rude staff who told me I might as well eat a dish I hadn't ordered as I was going to be charged for it anyway, and though food is good it is not a patch on the Sydney version.
Is this your business?