I was also going to suggest Argentina. Buenos Aires has lots to see and do including seeing gauchos at the FerÃa De Mataderos, experiencing a Tango, visiting Palermo, checking out the National Museum of Fine Arts, as well as traveling to Iguazu Falls (spectacular), and then heading across Rio de la Plata on a boat to see Montevideo, Uruguay, as well as its beautiful resort city of Punta del Este or even Piriapolis. Of course, Argentina is heading into winter now, so the weather won't be the best.
A second choice would be Los Cabos, Mexico, which includes the resort cities of Cabo San Lucas and San Jose del Cabo on the southern tip of Baja California. Actually, these are trips that I would like to make myself, so I'm living vicariously through your travels.
Problemaddict: It sounds like you are quite familiar with Argentina. When were you down there?