[Check my site in a few months for many more pictures of architecture in Brazil, including much more Niemeyer. For now you can also take my Architecture Quiz.]

The Memorial dos Povos Indigenas (Memorial for the Indigenous People), and the Catedral Militar, Igreja de N.S. da Paz
These are both located west of the television tower, in the area between the two branches of the Monumental Axis.

The Memorial dos Povos Indigenas (Memorial for the Indigenous People) (Memorial for the Indigenous People):

Catedral Militar, Igreja de N.S. da Paz: