The best source for theater, dance, film, and arts information is the "Viva" entertainment section of the Spanish-language daily La Nación. The paper also publishes the "Tiempo Libre" section each Friday, highlighting what's going on over the weekend. GAM Cultural is a free monthly flyer found in many upscale hotels and restaurants, and publishes features about what's going on around town. Listings in both publications are in Spanish but are easy to decipher.
Unfortunately, arts offerings in the city are nearly nonexistent during the high-season weeks from mid-December through early February. That's school vacation time.