Lately Nam Son has been our go-to vietnamese place. Not because it's particularly good (I haven't found a truly outstanding vietnamese place in NYC yet) but because it offers vegetarian spring and summer rolls for my vegetarian daughter and has a fairly wide-ranging menu. However, there is one dish there that I think is truly stellar--the whole fried fish with chilies and lemongrass. We usually order the red snapper and it comes to the table perfectly fried and showered with a mince of sauteed peppers and lemongrass. In a perfect world the chilies would be a touch hotter, but it's pretty addictive as it is.
I've never had this dish at any other NYC vietnamese restaurant, so there may be better versions out there. If there are, I would love to hear about them.
Also better than average at Nam Son is the grilled beef in grape leaves.
245 Grand St, New York, NY 10002