Here are some sites that I’ve used or learned about. As with anything that involves people’s opinion, this shouldn’t be your only source but it’s a good reference.
http://www.yelp.com (popular in the UK as well!)
http://www.guiaoleo.com.ar It’s in spanish but you can input the link in google translate!
http://www.burrp.com We didn’t use this site much as we had friends that suggested places to us.
http://www.openrice.com Reviews in English and Chinese
http://www.yup.vn I haven’t tried it but hope to when I eventually visit Vietnam!
Chilango is what folks from Mexico City are called. Kind alike in Buenos Aires they are called Portenos.