Bus 86 connects the airport to Plaza de Mayo in the center of the city, or take a taxi from one of the authorized taxi stands outside your terminal (journey time: 45 minutes).

The fastest and cheapest way to get around the city is by metro (the "subte"), but Buenos Aires is also great for walking. All of the main tourist and commercial areas are connected by the metro lines, except for the Recoleta and Puerto Madero neighborhoods, although they're just a short walk away from several stations -- Puerto Madero from the L.N. Alem stop on the B line, and Recoleta from Barrio Norte on the D line.

If you're going to visit more of Argentina, find the cheapest car rental rates here.