I was in BA in 2010, so I don't have much useful info at this point other than to highly recommend a trip to Iguazu Falls, which I thought was one of the most beautiful and impressive places I've ever been. You could probably do it in a (long) day, but it's about an hour flight. We stayed one night there and visited the Argentine side one day and the Brazilian side the other day. At the time U.S. citizens needed a visa to visit Brazil (not sure if that's changed), and we thought it was worth the hassle of getting the visa to see the Brazilian side as well as the Argentine side. We also needed a yellow fever vaccine for Brazil.