Minha sugestão de sources.list para o Debian 7 (Wheezy)

Utilizando apenas softwares 100% livres.

Após entrar no terminal como root
#nano /etc/apt/sources.list

Copiar o conteúdo entre as linhas

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deb http://ftp.br.debian.org/debian wheezy main
#deb-src http://ftp.br.debian.org/debian wheezy main

deb http://ftp.debian.org/debian/ wheezy-updates main
#deb-src http://ftp.debian.org/debian/ wheezy-updates main

deb http://security.debian.org/ wheezy/updates main
#deb-src http://security.debian.org/ wheezy/updates main
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