The main option and easily the most reliable is Aerolineas Argentinas/Austral http://www.aerolineas.com.ar,
who operate mostly B737-200s on the route or very occasionally, an MD
-80. It's a 40 minute flight, and typically costs US$100 return.
Alternatively, if you are feeling a little more adventurous, for a similar price you can fly on the military airline LADE http://www.lade.com.ar,
on either an F27 or an F28. Schedules are prone to last minute changes (or even cancellations) however, so attractive though they may look, I'd recommend AR
on balance, whose service is pretty good in any case.
Last year there were twice as many options, but Southern Winds pulled out and Aerovip folded...