Very interesting. Here in the SF Bay Area that would definitely be Napa Cabbage (not sure if that name comes from our Napa wine country), even in Asian markets.
Great thread idea though - looking forward to more!
ETA: It does not have anything to do with the wine country. According to Wikipedia: The word "napa" in the name napa cabbage comes from colloquial and regional Japanese, where nappa (菜っ葉) refers to the leaves of any vegetable, especially when used as food.