On the topic of restaurants in general, if you're looking for a certain type of cuisine or restaurant there are two great sites I use:
http://www.guiaoleo.com.ar/http://www.saltshaker.net/Guia is in Spanish but has tons of great restaurant reviews, and if you're an English-speaking tourist Salt Shaker has you covered. They're how I find most of my places to try!
Suerte, Evan