Fly from New York to Buenos Aires, Argentina for $615 round-trip, including all taxes, on TAM.
This one is pretty scarce, and we found it to be available only on a couple of dates in May (for example, the 15th through the 23rd, as seen in the screen grab below via Orbitz). This one will surely go fast, so you might want to pounce as soon as possible. We found similarly low fares on other dates for $682.
The next best fare we spotted along this route for spring is $832, travel April through June, with higher availability.