I'd be interested in people's recommendations of specific brands and varieties of frozen items. I have a few favorites of my own. None are perfect but they are decent.
Golden Treasure dumplings--smallish, with the slightly thicker skins (I don't like the skins that are almost brittle)
Sasum Deer Korean style dumplings--these are very small and very reminiscent of Chinese style water dumplings
Doll "shrimp" wontons--more bamboo shoots and mushrooms than shrimp, but nicely flavored and oh so convenient to throw into a noodle soup
I'd be particularly interested in steamed bun suggestions. I've yet to find one that I really like.