I'd say there are two essential Chico Buarque albums to start with, though there are many more good ones. Construcao, which is one of his most adventurous, and Meus Caros Amigos, which has a number of his best known songs, great melodies (but unfortunately is hard to find). Also check out the Lumiar songbooks for lots of great singers doing his material.
I'm not as big on Lobo, so no suggestions, though Chico & he did several projects together.
Well, just realized that I was responding to a 4-year-old query.
Has Alaide Costa been mentioned? I put her in the same class as Billie Holiday, Edith Piaf, Amalia Rodrigues & Cesaria Evora, if you know what I mean...