If you can get to Iguazu Falls (on Argentina/Brazil border) absolutely do it - and there is at least one casino around there for some chips.

Iguazu Falls is amazing (where they filmed The Mission). I've been to Victoria Falls in Zimbabwe and Niagra in New York State - but in my opinion, Iguazu is the most amazing.

Of course, Rio is a must if you're in Brazil - I'm sure that's already included.