I buy from Ebay quite a bit. It's easy to scale down your search to size, NWT or whatever.
Abercrombie & Fitch in the US as our dollar is great against theirs at the moment and they ship to Australia.
Zodee, Intimo.
It's been a while! You can shop Jeans West online now too.
The other thing I do is look through magazines like Marie Claire or Maddison and check out their shopping pages as they have all the web site address for the clothes and then go and check them out. Not all of them are expensive designers either.
Ozsale is another good one.
You can get Lorna Jane online now too.