Reuni alguns repositórios muito úteis para o Ubuntu, a maioria deles para Ubuntu 9.10. Todo o processo de adicionar os repositórios é feito pelo terminal (muito mais prático). Segue a lista:

Webmin (administração de servidores baseados em Unix com interface web)

sudo sh -c 'echo "deb http://download.webmin.com/download/repository sarge contrib" >> /etc/apt/sources.list'

Emesene (mensageiro instantâneo)

sudo sh -c 'echo "deb http://apt.emesene.org/ ./" >> /etc/apt/sources.list'

QBitTorrent (cliente BitTorrent)

sudo sh -c 'echo "deb http://ppa.launchpad.net/hydr0g3n/ppa/ubuntu jaunty main" >> /etc/apt/sources.list'
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 47B4D1C4
sudo apt-get update && sudo apt-get install qbittorrent

Opera (navegador)

sudo sh -c 'echo "deb http://deb.opera.com/opera-beta/ stable non-free" >> /etc/apt/sources.list'
sudo wget -O - http://deb.opera.com/archive.key | sudo apt-key add -

XMMS (clone do Winamp para Linux)

sudo sh -c 'echo "deb http://www.pvv.ntnu.no/~knuta/xmms/karmic ./" >> /etc/apt/sources.list'

Cafuego (SecondLife, firmwares Broadcom, Inkscape…;)

wget -q -O - http://ubuntu.cafuego.net/cafuego.gpg | sudo apt-key add -
sudo sh -c 'echo "deb http://ubuntu.cafuego.net/ jaunty-cafuego all" >> /etc/apt/sources.list'

Ubuntu Satanic (versão satânica do Ubuntu, inútil, só achei interessante)

wget -q http://ubuntusatanic.org/ubuntu-se-key.gpg -O- | sudo apt-key add -
sudo sh -c 'echo "deb http://ubuntusatanic.org/hell karmic main" >> /etc/apt/sources.list'

VirtualBox (máquina virtual)

sudo sh -c 'echo "deb http://download.virtualbox.org/virtualbox/debian karmic non-free" >> /etc/apt/sources.list'
wget http://download.virtualbox.org/virtualbox/debian/sun_vbox.asc
sudo apt-key add sun_vbox.asc

DropBox (backup remoto)

sudo sh -c 'echo "deb http://linux.dropbox.com/ubuntu karmic main" >> /etc/apt/sources.list'
gpg --keyserver pgp.mit.edu --recv-keys 3565780E

Wicd (gerenciador de rede)

sudo sh -c 'echo "deb http://apt.wicd.net jaunty extras" >> /etc/apt/sources.list'
wget -q http://apt.wicd.net/wicd.gpg -O- | sudo apt-key add -

PlayOnLinux (instalador de jogos e softwares Windows para Linux)

sudo wget http://deb.playonlinux.com/playonlinux_karmic.list -O /etc/apt/sources.list.d/playonlinux.list

UbuntuGames (diversos games)

sudo sh -c 'echo "deb http://archive.ubuntugames.org ubuntugames main" >> /etc/apt/sources.list'

CompizFusion (efeitos gráficos)

sudo sh -c 'echo "deb http://ppa.launchpad.net/compiz/ppa/ubuntu karmic main multiverse restricted universe" >> /etc/apt/sources.list'

Gwibber (cliente de redes sociais)

sudo sh -c 'echo "deb http://ppa.launchpad.net/gwibber-daily/ppa/ubuntu karmic main universe restricted multiverse" >> /etc/apt/sources.list'

aMSN (mensageiro instantâneo)

sudo sh -c 'echo "deb http://ppa.launchpad.net/amsn-daily/ppa/ubuntu karmic main" >> /etc/apt/sources.list'

Gnome-Do (similar ao Katapult do KDE)

sudo sh -c 'echo "deb http://ppa.launchpad.net/do-core/ppa/ubuntu karmic main" >> /etc/apt/sources.list'

Ubuntu Tweak (diversos ajustes não disponíveis na interface gráfica)

sudo sh -c 'echo "deb http://ppa.launchpad.net/tualatrix/ppa/ubuntu karmic main multiverse restricted universe" >> /etc/apt/sources.list'

Medibuntu (Multimídia)

sudo wget --output-document=/etc/apt/sources.list.d/medibuntu.list http://www.medibuntu.org/sources.list.d/$(lsb_release -cs).list && sudo apt-get --quiet update && sudo apt-get --yes --quiet --allow-unauthenticated install medibuntu-keyring && sudo apt-get --quiet update

SwitFox (clone do Firefox)

sudo sh -c 'echo "deb http://getswiftfox.com/builds/debian unstable non-free" >> /etc/apt/sources.list'

Last.fm (scrobbler da Last.fm)

wget http://apt.last.fm/last.fm.repo.gpg -O- | sudo apt-key add -
sudo sh -c 'echo "deb http://apt.last.fm/ debian stable" >> /etc/apt/sources.list'

aMule (cliente P2P)

gpg --keyserver wwwkeys.eu.pgp.net --recv 50D0AE60
gpg --armor --export 50D0AE60 | sudo apt-key add -
sudo sh -c 'echo "deb http://www.vollstreckernet.de/debian/ stable amule wx" >> /etc/apt/sources.list'

Skype (mensageiro)

sudo sh -c 'echo "deb http://download.skype.com/linux/repos/debian/ stable non-free" >> /etc/apt/sources.list'

Google

sudo sh -c 'echo "deb http://dl.google.com/linux/deb/ stable non-free" >> /etc/apt/sources.list'

Wine (roda aplicativos Windows no Linux)

gpg --keyserver subkeys.pgp.net --recv 387EE263
gpg --export --armor 387EE263 | sudo apt-key add -
sudo sh -c 'echo "deb http://wine.budgetdedicated.com/apt karmic main" >> /etc/apt/sources.list'

VLC (reproduz arquivos multimídia)

sudo add-apt-repository ppa:c-korn/vlc