There are two churrascaria in Manhattan, Rio (43rd between 6th & Bwy) and Platforma (49th between 8&9 Ave)
There is small nice place called Rice'n'Beans in 51/52nd on 9th Ave. that we go from time to time.
There are one or two uneven restaurants in Little Brazil (46th between 5th & 6th Ave) the names of who excapes me at this time.
Whatever you do, do not, I repeat do not, go to the irredeemably bland and boring Viva Brasil on Amsterdam in the 80s. The menu reads really well and then it's all down hill from there.
There's a cute little place in the West Village called Casa (on Bedford Street). The food is kind of inconsistent - some wonderful things, some "huh?"s - but it's very intimate, friendly and laid back. And the caparainha's rock.
I know there are several in town, but the only one I've been to (and enjoyed) is Plataforma Churascaria at 316 W. 49th St. It's prix fixe, all you can eat. There's a huge salad bar (both hot and cold foods), followed by a parade of roasted meats. Good food, not GREAT, and good value. There's live music some evenings.