Compartilho aqui a souces.list que estou utilizando no momento em meu Debian Squeeze. Nela há repositórios como o da Google (para instalar o Google Chrome, Picasa, etc), do Skype, do Ópera, Frostwire (um fork do Limewire), Virtualbox, etc.
As linhas com a cerquilha na frente (#) significa que estão comentadas e não serão utilizadas. As mirros de segurança e oficiais estão duplicadas com espelhos nacionais e internacionais; prefira os espelhos nacionais, mas pode ocorrer deles virem a ficarem fora do ar por algum tempo e ter outra opção é uma mão na roda. Como podem ver, ela está bem completa, mas não utilizo todas as fontes. Fica a seu critério e gosto.
#Sources.list
#para usar os servidores abaixo basta remover o "#" e atualizar a lista de pacotes
#Mirros de segurança
deb http://ftp.br.debian.org/debian-security/ squeeze/updates main contrib non-free
deb-src http://ftp.br.debian.org/debian-security/ squeeze/updates main contrib non-free
#deb http://security.debian.org/ squeeze/updates main contrib non-free
#deb-src http://security.debian.org/ squeeze/updates main contrib non-free
#Debian Squeeze updates
deb http://ftp.br.debian.org/debian/ squeeze-updates main contrib non-free
#deb-src ftp://ftp.br.debian.org/debian/ squeeze-updates main contrib non-free
#Mirros oficiais
deb ftp://ftp.br.debian.org/debian/ squeeze main contrib non-free
deb-src ftp://ftp.br.debian.org/debian/ squeeze main contrib non-free
#deb http://linorg.usp.br/debian/ squeeze main contrib non-free
#deb ftp://ftp.us.debian.org/debian/ squeeze main contrib non-free
#deb-src ftp://ftp.us.debian.org/debian/ squeeze main contrib non-free
#Proposed updates
deb http://ftp.br.debian.org/debian squeeze-proposed-updates main contrib non-free
#deb-src http://ftp.br.debian.org/debian squeeze-proposed-updates main contrib non-free
#Mirros volatile
#Esse mirro foi descontinuado. Veja mais em http://goo.gl/URYi9
#deb http://volatile.debian.org/debian-volatile squeeze/volatile main
#deb-src http://volatile.debian.org/debian-volatile squeeze/volatile main
#Debian Unofficial - http://debian-unofficial.org/
#Para a chave gpg, execute o comando: aptitude install debian-unofficial-archive-keyring
#deb http://unofficial.debian-maintainers.org/ squeeze main contrib non-free restricted
#deb-src http://unofficial.debian-maintainers.org/ squeeze main contrib non-free restricted
#Mirro kernel
#deb ftp://mirrors.kernel.org/debian/ squeeze main contrib non-free
#deb-src ftp://mirros.kernel.org/debian/ squeeze main contrib non-free
#Mirros multimidia
#Para a chave gpg, execute o comando: aptitude update && aptitude install debian-multimedia-keyring && aptitude update
deb http://deb-multimedia.org/ squeeze main non-free
#deb-src http://www.debian-multimedia.org squeeze main non-free
#deb http://ftp.br.debian.org/debian-multimedia/ squeeze main
#deb-src http://ftp.br.debian.org/debian-multimedia squeeze main
deb http://mozilla.debian.net/ squeeze-backports iceweasel-release
#Opera
#Para a chave gpg, execute o comando: wget -O - http://deb.opera.com/archive.key | sudo apt-key add -
#deb http://deb.opera.com/opera/ squeeze non-free
#deb-src http://deb.opera.com/opera/ squeeze non-free
#Skype
#Para a chave gpg, execute o comando: gpg --keyserver pgp.mit.edu --rec-keys 0xd66b746e && gpg --export --armor 0xd66b746e | apt-key add -
deb http://download.skype.com/linux/repos/debian/ stable non-free
#deb-src http://download.skype.com/linux/repos/debian/ stable non-free
#Frostwire (KEY=EFD17969)
#deb http://apt.debianchile.org/frostwire squeeze main
#deb-src http://apt.debianchile.org/frostwire squeeze main
#Esmka - programa para enviar torpedos msn gratuítamente
#Para a chave gpg, execute o comando: wget -q -O - http://repo.palatinus.cz/repo.key | apt-key add -
#deb http://repo.palatinus.cz/stable /
#deb-src http://repo.palatinus.cz/stable /
# Cairo-Dock-Squeeze
# Para a chave gpg, execute o comando: wget -q http://repository.glx-dock.org/cairo-dock.gpg -O- | apt-key add -
#deb http://repository.glx-dock.org/debian unstable cairo-dock
# Enlightement (Um gerenciador de janelas leve e moderno)
# Para a chave gpg, execute o comando: wget -q http://packages.enlightenment.org/repo.key -O- | apt-key add -
# Se o primeiro arquivo não funcionar, pegar repo.key.old no mesmo link.
#deb http://packages.enlightenment.org/debian squeeze main extras
#deb-src http://packages.enlightenment.org/debian squeeze main extras
#deb-src http://ftp.br.debian.org/debian squeeze-proposed-updates main contrib non-free
#Mirros volatile
#Esse mirro foi descontinuado. Veja mais em http://goo.gl/URYi9
#Backports
deb http://backports.debian.org/debian-backports squeeze-backports main contrib non-free
#deb-src http://backports.debian.org/debian-backports squeeze-backports main contrib non-free
#Para a chave gpg, execute o comando: aptitude install debian-unofficial-archive-keyring
#deb http://unofficial.debian-maintainers.org/ squeeze main contrib non-free restricted
#deb-src http://unofficial.debian-maintainers.org/ squeeze main contrib non-free restricted
#Mirro kernel
#deb ftp://mirrors.kernel.org/debian/ squeeze main contrib non-free
#deb-src ftp://mirros.kernel.org/debian/ squeeze main contrib non-free
#Mirros multimidia
#Para a chave gpg, execute o comando: aptitude update && aptitude install debian-multimedia-keyring && aptitude update
deb http://deb-multimedia.org/ squeeze main non-free
#deb-src http://www.debian-multimedia.org squeeze main non-free
#deb http://ftp.br.debian.org/debian-multimedia/ squeeze main
#deb-src http://ftp.br.debian.org/debian-multimedia squeeze main
#Backport Iceweasel corrente
#Para a chave gpg, execute o comando: gpg key: wget -q http://mozilla.debian.net/archive.asc -O- | apt-key add -deb http://mozilla.debian.net/ squeeze-backports iceweasel-release
#Google Repositore
#Para a chave gpg, execute o comando: wget -q -O - https://dl-ssl.google.com/linux/linux_signing_key.pub | sudo apt-key add -
#Para a chave gpg, execute o comando: wget -q -O - https://dl-ssl.google.com/linux/linux_signing_key.pub | sudo apt-key add -
deb http://dl.google.com/linux/deb/ stable non-free
#deb-src http://dl.google.com/linux/deb/ stable non-free
#deb-src http://dl.google.com/linux/deb/ stable non-free
#Chromium launchpad
#Para a chave gpg, execute o comando:
apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 4E5E17B5
#deb http://ppa.launchpad.net/chromium-daily/ppa/ubuntu lucid main #versão em testes
deb http://ppa.launchpad.net/chromium-daily/stable/ubuntu lucid main #versão corrente
#Opera
#Para a chave gpg, execute o comando: wget -O - http://deb.opera.com/archive.key | sudo apt-key add -
#deb http://deb.opera.com/opera/ squeeze non-free
#deb-src http://deb.opera.com/opera/ squeeze non-free
# Wine
# Para a chave gpg, execute o comando: wget -O - http://www.lamaresh.net/apt/key.gpg | apt-key add -
#deb http://www.lamaresh.net/apt/ squeeze main
#deb-src http://www.lamaresh.net/apt/ squeeze main
# Virtualbox
#Para a chave gpg, execute o comando: wget -q http://download.virtualbox.org/virtualbox/debian/sun_vbox.asc -O- | sudo apt-key add -
#deb http://download.virtualbox.org/virtualbox/debian squeeze non-free
#deb-src http://download.virtualbox.org/virtualbox/debian squeeze non-free
# Dropbox
#Para a chave gpg, execute o comando: apt-key adv --keyserver pgp.mit.edu --recv-keys 5044912E
# deb http://dropbox.nwlinux.us lucid main
#Skype
#Para a chave gpg, execute o comando: gpg --keyserver pgp.mit.edu --rec-keys 0xd66b746e && gpg --export --armor 0xd66b746e | apt-key add -
deb http://download.skype.com/linux/repos/debian/ stable non-free
#deb-src http://download.skype.com/linux/repos/debian/ stable non-free
#Frostwire (KEY=EFD17969)
#deb http://apt.debianchile.org/frostwire squeeze main
#deb-src http://apt.debianchile.org/frostwire squeeze main
#Esmka - programa para enviar torpedos msn gratuítamente
#Para a chave gpg, execute o comando: wget -q -O - http://repo.palatinus.cz/repo.key | apt-key add -
#deb http://repo.palatinus.cz/stable /
#deb-src http://repo.palatinus.cz/stable /
# Cairo-Dock-Squeeze
# Para a chave gpg, execute o comando: wget -q http://repository.glx-dock.org/cairo-dock.gpg -O- | apt-key add -
#deb http://repository.glx-dock.org/debian unstable cairo-dock
# Enlightement (Um gerenciador de janelas leve e moderno)
# Para a chave gpg, execute o comando: wget -q http://packages.enlightenment.org/repo.key -O- | apt-key add -
# Se o primeiro arquivo não funcionar, pegar repo.key.old no mesmo link.
#deb http://packages.enlightenment.org/debian squeeze main extras
#deb-src http://packages.enlightenment.org/debian squeeze main extras