I really enjoyed Siga La Vaca in Puerto Madero. For REALLY cheap, you can get all you can eat asado (grilled meats), unlimited access to their salad bar (which is VERY extensive) and soda or a BOTTLE of wine! Everything was really fresh and delicious. We left very happy and full!

We went to BA last October for our honeymoon. We stayed in Palermo Soho, so most of my recos are from that area. Here's a few places we found: La Cabrera (highly, highly recommend this place for steak. here's the site: http://www.parrillalacabrera.com.ar/) also they have a sister restaurant called Sucre. Another recommendation is Lo de Jesus, but I've heard people have had mixed experiences there. Alvear Palace is a super fancy hotel, but they have a great brunch if you're willing to splurge (http://alvearpalace.com/v3/eng/index.php?secc=restaurantes&resto=brunch&PHPSESSID=ac4ca302fc833c777908577757d9c777). Also, the famous coffee shop is a must-see: http://www.cafetortoni.com.ar/. Hope that helps. I'm jealous. We had an amazing time there.