Branching use of "USA" and "United States"

[Joe Marraffino]

I'd like to filter a search by country. Right now the easiest way to do this is to include the country's name as a search term. In doing so I found that

216 entries are in the United States, and
39 entries are in the USA

For the sake of future internationalization, I think it would be useful to have the country location field to be chosen from a list, rather than having people spell it out.