Here's some fairly normalized models for representing postal addresses. Making postal_code a separate model would probably be the only way to get it to a level that everyone would agree is 2NF, but we handle a lot of international addresses so that isn't really feasible.
Country and StateProvince are intended to be populated with data from ISO 3166. I'd include the SQL I used with that data, but it's very long and there's no attach feature. Also, I'd probably be violating ISO's copyright.