I had dinner at Din Tai Fung, and it was so good, I went back for lunch the next day. This place is more expensive than many dim sum restaurants...not sure it's worth the premium, but it was near my hotel and I really enjoyed my meals.
The xiao long bao were truly excellent. Great wrappers and fantastic filling...full of flavor but not greasy.
The steamed pork buns were also a highlight, as were the spicy wontons.
There are a couple of locations in Hong Kong. The one I visited was in Causeway Bay, just a few blocks from the Causeway Bay MTR station.