Apologies in advance as I couldn't figure out how to send a PM (is there a way?) on this site.
Anyway, vinhotinto, loved your recs for Lisbon so much that I wondered if I might trouble you to provide some favorites for Sao Paulo, since you indicated you spend time in Brazil too. I'm over here now and trying to find the kinds of places you so easily ID'd in Lisbon.
I know this is Spain/Portugal but I couldn't figure out any other way to do this, as you don't seem to post in the Brazil sections.
Here are some of my recommendations located in the zona sul, centro, and zona norte. Many of these places are Carioca institutions that serve large portions and specialize in luso-brazilian cuisine. Granted, these are not the most upscale of places, but you are bound to always get a reliable and affordable meal at these places. I tend to favor the centro and zona norte as you can tell from below, but have thrown in some zona sul places too!
Boteco Casual (Centro)
Casual Retrô (Centro)
Bar Luiz (Centro)
Adega Flor de Coimba (Lapa)
Da Silva (Ipanema and Centro)
Nova Capela (Lapa)
Lamas (Flamengo/Largo do Machado)
Siri (Vila Isbael)
Bistrô Senac (Flamengo)
Boa Viagem e Boa Sorte!