Since 1992, I have been working for several  projects and Non-Governmental Organizations in Rio de Janeiro. Environmental NGOs are very active in the WEB and they have rich sites, usually updated often and with lots of useful  information. My favorite Brazilian Organizations are:

Alfredo Sirkis - Website current secretary of Urbanism of Rio de Janeiro, and part of the history of the environmental movement in Brazil
Ibase This is the mother of all NGOs in Brazil. Well, maybe not, but they are the backbone
GRUDE Friends and great activists.
Instituto Socioambiental A think tank on Brazilian Forests and Native People.
Greenpeace Brazil the are still great

Instituto de Estudos da Religião: ISER’s Environmental program is the reference for anything on Agenda 21 in Brazil.

Viva Rio Home Page It is worth visiting them. Campaings against violence, human rights, citizenship, something for everybody.