I'll be staying in the suburbs with family friends (US expats). Want to take them to dinner as a thank you (and as an excuse to see the best of Sao Paulo, which is supposedly a dining mecca). Any recommendation? This will be in a couple weeks at the end of January if that helps with reservation timing. Probably prefer something with a more traditional menu to a really long tasting. Local flavor would be nice as well if possible.
Brasil a Gosto is one of my favorite restaurants in Sao Paulo. It's traditional Brazilian food treated in a nouvelle cuisine style. It's not cheap but not as expensive as DOM, Fasano and Gero, which are also very good. People are not as big in reservations in Brasil as they are in the US... we are not that organized :) Most places don't even take reservations but the more upscale ones will. You can check Brasil a Gosto website: http://www.brasilagosto.com.br/. They have an English version.
Attimo is FANTASTIC. In the top 5 meals of my entire life. We ate at 50+ places in Sao Paulo and it's still one of the most memorable. The chef, Jefferson Rueda, just won the chef of the year award. He cooks Italian-Brazilian food and does magic with the most humble ingredients - anything you order there will be amazing. It's very true to the roots of the Italian immigrants and is definitely different from your standard Italian restaurant. We actually just made a video about our experience there: http://www.youtube.com/watch?v=u84ihL...
Other top picks by us are Brasil a Gosto (as Toog already listed) and Epice - a really innovative french/local cuisine.
And more international cuisine would be Kinoshita for Japanese (they have a really reasonable executive lunch menu) and Ici bistro for french (also good executive lunch menu)
At Epice, you can also try the lunch menu, tuesdays to fridays (it's very busy cause it's a bargain. 2 options of first, second course and dessert, last time I went in december it was less than 40 brazilian reais, free water and amuse-bouches). The Picture is from that meal. If you have instagram, you can check more pictures at mine, @foodemotion