Yue-Wah has the most extensive selection of "ethnic" foods in Madison. I like how their aisles are divided into different sections by nationality ("ie--Japanese, Indonesian, etc) so it's easier to find ingredients for different cuisines. In addition to Asian foods, they carry Jamaican, Middle Eastern, and Latino foods.
Others here have commented on the customer service here, but frankly, I don't expect customer service here the same way I would expect CS at say, Trader Joe's. I say check this place out if looking for Asian foods. Unlike MIdway Asian Foods, there is not a significant amount of traditional "American" food here so there's lots to look at.