Here is a starter and I am sure others with offer some good suggestions too
Bar 6 (lunch) -Armenia 1676, Gran Bar Danzon (wine bar, tapas) -Libertad 1161 piso 1, Olsen's (for Sunday Brunch) -Gorriti 5870, Sucre -Sucre 676, Sudestada -Guatemala 5602, La Brigada-Peña 2475 (great steaks). Juana M, -Carlos Pellegrini 1535 ,El Trapiche (old world great food, a must) Paraguay 5599, and the cafe at the MALBA is a great place for an afternoon coffee or lite lunch. I must add this one - Bo Bo (Bo Bo Hotel) Guatemala 4882 y Thames Tel: 4774-0505. It is so good, has become one of my favorites. For a "scene" the ulitmate see and be see place it is Casa Cruz Uriarte 1658. Or it used to be anyway..

Hope this helps and have a great trip down.
Sam