Palacio Barolo is the best place to capture panoramic views of Buenos Aires.  It is located on Avenida de Mayo between Avenida 9 de Julio and Plaza de Congresso at Av. de Mayo 1370. There is no sign that says "Palacio Barolo" in the front, so make sure you know the address or at least what the building looks like. You can also just ask anyone on the street if you're not sure. The tour provides the unique history of the building which was themed around Dante's Inferno.  Towards the end of the tour you are taken to the top of the building where you can take pictures from several small balconies around the top tower.  Be warned.  This is not for people with a fear of heights as the balconies are outdoors.  However you can still enjoy the views from inside the tower without actually having to step outside. What makes this so unique is that there is probably no other place offering the views of Buenos Aires than Palacio Barolo.

Bilingual English/Spanish tours are offered Monday and Thursday every hour on the hour from 4 to 7 pm in either English or Spanish. On Wednesdays and Fridays, there is a nighttime tour at 8 pm, Thursdays at 8:30pm, which includes the lighthouse and wine. Enter the building and ask the guard at the front desk to find the ticket booth in the lobby. The cost is $50 pesos for the afternoon tour and $95 pesos for the nighttime tour. 

Official website for guided tours (in English)

Main home page for tours (Spanish, English, Italian - at bottom of page)