This museum is located in Recoleta and it is free! The museum host works by Goya, Picasso, Monet, Rodin, Van Gogh, and many more. The Museum's 11,000 piece collection includes works from 18th and 19th century European, and Argentine artists.
You can also go to the new MALBA ( Museum of Latin American Art) Which has an extesive collection of Latine American artists. http://www.malba.org.ar/web/home.php
There is a new museum that just opened up located in the chic Puerto Madero district. Coleccion de arte Amalia Lacroze de Fortabat Museum is a modern cement structure that houses a collection of art from Amalia Lacroze collection. Locroze de Fortabat was a wealthy industrialist. The colections include: Warhol, Dali, Brueghel and Klimt. Also included are Argentine and Latin American artists. http://www.coleccionfortabat.org.ar/
Portrait of Sra. Amalia Lacroze de Foratbat by Andy Warhol
There are many museums in Buenos Aires. The National Museum of Fine Arts, is free and cannot be missedhttp://www.info-recoleta.com/museo-nacional-bellas-artes.html