I've been in Argentina for almost two months and finally found some decent beers. Quilmes and Brahma and friends are, frankly, not going to cut it for me.
Buller Brewing Company
The first place that was recommended to me was Buller Brewing Company (ratebeer review) which turned out to be pretty good. They have a selection of about 8 beers which were all decent, though none were really amazing. The dry stout was probably the best variety that they had. I went to the location near Recoleta cemetery which of course is a nice tourist area on its own.
Cossab Cerveza Artesanal
In a non touristy location is Cossab - at Carlos Calvo 4199 - which is just a standard corner bar which happens to serve hundreds of local and international beers. The international selection is dominated by Dutch/Belgian varieties and a few standards (Guinnes - duh). In addition to great beers, Cossab also has quite good food including a Wednesday Night "Pizza Libre" night where "Libre" means all you can eat instead of just "free". For 10 Pesos, it's a good deal.
Bangalore Indian Restaurant - Stone IPA (cask style)
Without looking for beer, but just Indian food, we happened upon Bangalor (4990 Humboldt in Palermo) which serves not only delicious Indian curries but also several Stone offerings including a stout, an XB (extra bitter?) and a "cask style" IPA (not as cold and not so bubbly). Since Stone IPA is one of my favorites I was said to find that the cask style version is not as good...but all the same it's a great find.
More Argentine Beers
Overall, the best guide I've found is the list from ratebeer.com which covers Argentina. Though it would be nice if ratebeer.com's listings were broken down by cities where the beers are available.