1500kms from Buenos Aires is the historic capital of Salta. There are numerous interesting buildings including the neoclassical Iglesia San Francisco. There are several notable scenic excursions close by such as the 'train to the clouds' (tren a las nubes) which unfortunately is closed for restoration until 2008, but you can take almost the same route by car, since the road criss crosses the railway line and the scenery is pretty good.
North of the train/car route to the clouds is the huge salt flats of Salinas Grandes where you can traverse tracks to the center of the flats and see where the salt is extracted from rectangles dug into the ground and piled into mounds.
I don't think I'll be applying for a job here however as they pay the workers 40 pesos per tonne of salt extracted and many of the workers eventually go blind from exposure to the harsh elements of sun, wind, salt and dust.