It holds quite a large domestic market to nearly all parts of Brazil due to its central location. You can fly to nearly any Brazilian city from Brasilia thorugh Varig, TAM, Vasp, Transbrasil(based in Brasilia), Nordeste, Rio-Sul, and many others. I am unaware of any Intl' flights from Brasilia, but I am almost sure that they offer one stop(if not non-stop) service to palces like Buenos Aires, or Santiago, and they do also have one-stop service to Miami, and possibly New York.
TAM Meridional has tried to set up what they call a "hub" in Asuncion, with flights to Buenos Aires, Montevideo, Lima, and Sao Paulo. I think they also fly to other points in Argentina, such as Cordoba and Rosario. Other Int'l carriers at Asuncion include American Airlines(operating 767-300 with direct service to Miami via Sao Paulo), Varig(737 to Sao Paulo, and Rio?), and Aerolineas Argentinas(no info)