First thing you should do is make a backup copy of your current /etc/apt/sources.list by doing the following command:

sudo cp -a /etc/apt/sources.list /etc/apt/sources.list.old

Once you do that and perform the gpg commands at the bottom of this post as well, you'll want to immediately perform the following commands:

sudo apt-get update && sudo apt-get upgrade

If you want to update any kernels or major things like that then run the following command instead:

sudo apt-get update && sudo apt-get dist-upgrade

Many of the repos listed below are commented out with a # at the beginning of the line. If you wish to use any of those repos, you need to remove the # and perform the following command immediately afterwards:

sudo apt-get update

Then open up your favorite editor as root user and copy/paste the following code into the editor and save the file as /etc/apt/sources.list An example of this would be to use the following command:

kdesu kwrite /etc/apt/sources.list

You can replace 'kwrite' with your favorite editor. If you want to do it with a CLI editor, then use this command:

sudo vi /etc/apt/sources.list

Copy and paste the information into the above mentioned file that you have open with your editor of choice:

# Automatically generated sources.list
# http://www.ubuntulinux.nl/source-o-matic
#
# If you get errors about missing keys, lookup the key in this file
# and run these commands (replace KEY with the key number)

# Ubuntu supported packages 
#(packages, GPG key: 437D05B5)
deb http://se.archive.ubuntu.com/ubuntu edgy main restricted
deb http://se.archive.ubuntu.com/ubuntu edgy-updates main restricted
deb http://security.ubuntu.com/ubuntu edgy-security main restricted

# Ubuntu supported packages 
#(sources, GPG key: 437D05B5)
deb-src http://se.archive.ubuntu.com/ubuntu edgy main restricted
deb-src http://se.archive.ubuntu.com/ubuntu edgy-updates main restricted
deb-src http://security.ubuntu.com/ubuntu edgy-security main restricted

# Ubuntu community supported packages 
#(packages, GPG key: 437D05B5)
deb http://se.archive.ubuntu.com/ubuntu edgy universe multiverse
deb http://se.archive.ubuntu.com/ubuntu edgy-updates universe multiverse
deb http://security.ubuntu.com/ubuntu edgy-security universe multiverse

# Ubuntu community supported packages 
#(sources, GPG key: 437D05B5)
deb-src http://se.archive.ubuntu.com/ubuntu edgy universe multiverse
deb-src http://se.archive.ubuntu.com/ubuntu edgy-updates universe multiverse
deb-src http://security.ubuntu.com/ubuntu edgy-security universe multiverse

# kubuntu.org packages for the latest KDE version 
#(packages, GPG key: DD4D5088)
#deb http://kubuntu.org/packages/kde-latest edgy main

# kubuntu.org packages for the latest Koffice version 
#(packages, GPG key: DD4D5088)
deb http://kubuntu.org/packages/koffice-latest edgy main

# kubuntu.org packages for the latest amaroK version 
#(packages, GPG key: DD4D5088)
deb http://kubuntu.org/packages/amarok-144 edgy main
deb-src http://kubuntu.org/packages/amarok-144 edgy main

# Bleeding edge wine packages (packages)
#deb http://wine.budgetdedicated.com/apt edgy main

# The Opera browser (packages)
deb http://deb.opera.com/opera etch non-free

# Bazaar-NG development 
#(packages, GPG key: 1F44842D)
#deb http://people.ubuntu.com/~jbailey/snapshot/bzr ./

#deb http://download.skype.com/linux/repos/debian/ stable non-free

#deb http://download.videolan.org/pub/videolan/debian/ sid main

## http 100mbit/s mirror provided thanks to OVH (http://ovh.com)
deb http://packages.freecontrib.org/plf/ edgy-plf free non-free
deb-src http://packages.freecontrib.org/plf/ edgy-plf free non-free

# seb128 repository (gaim - rhythmbox)
deb http://people.ubuntu.com/~seb128/deb ./

# Samba
#deb http://www.linux2go.dk/ubuntu edgy main

# Gauvain Repository
#deb http://gauvain.tuxfamily.org/repos edgy contrib
#deb-src http://gauvain.tuxfamily.org/repos edgy contrib

# superm1's repository v6.10
#deb http://home.eng.iastate.edu/~superm1 edgy all
#deb-src http://home.eng.iastate.edu/~superm1 edgy all
#deb http://home.eng.iastate.edu/~superm1 edgy lirc
#deb-src http://home.eng.iastate.edu/~superm1 edgy lirc
#deb http://home.eng.iastate.edu/~superm1 edgy mythtv
#deb-src http://home.eng.iastate.edu/~superm1 edgy mythtv
#deb http://home.eng.iastate.edu/~superm1 edgy non-free
#deb-src http://home.eng.iastate.edu/~superm1 edgy non-free
#deb http://home.eng.iastate.edu/~superm1 edgy other
#deb-src http://home.eng.iastate.edu/~superm1 edgy other

# Koffice latest
deb http://kubuntu.org/packages/koffice-latest edgy main

deb http://se.archive.ubuntu.com/ubuntu/ edgy-backports main 
deb http://se.archive.ubuntu.com/ubuntu/ restricted universe multiverse
#deb-src http://se.archive.ubuntu.com/ubuntu/ edgy-backports main
#deb-src http://se.archive.ubuntu.com/ubuntu/ restricted universe multiverse

# imbrandons personal repos
deb http://imbrandon.com/packages edgy amarok
deb http://imbrandon.com/packages edgy konversation-nightly

# SoS repos
deb http://SeerOfSouls.com/ edgy contrib
#deb-src http://SeerOfSouls.com/ edgy contrib
deb http://SeerOfSouls.com/ edgy e17
#deb-src http://SeerOfSouls.com/ edgy e17

# PLF REPOSITORY (Unsupported. May contain illegal packages. Use at own risk.)
deb http://packages.freecontrib.org/plf edgy-plf free non-free
deb-src http://packages.freecontrib.org/plf edgy-plf free non-free

And the gpg commands to import the keys are as follows:

You'll want to perform all of the following commands as root user:

gpg --keyserver subkeys.pgp.net --recv B0B7481B1F44842D && gpg --export 
--armor B0B7481B1F44842D | sudo apt-key add - 

gpg --keyserver subkeys.pgp.net --recv A506E6D4DD4D5088 && gpg --export 
--armor A506E6D4DD4D5088 | sudo apt-key add - 

gpg --keyserver subkeys.pgp.net --recv 49A120FD1135D466 && gpg --export 
--armor 49A120FD1135D466 | sudo apt-key add - 

gpg --keyserver subkeys.pgp.net --recv 4CF19C3233BAC1B3 && gpg --export 
--armor 4CF19C3233BAC1B3 | sudo apt-key add -

gpg --keyserver subkeys.pgp.net --recv 07DC563D1F41B907 && gpg --export 
--armor 07DC563D1F41B907 | sudo apt-key add -

gpg --keyserver subkeys.pgp.net --recv 31A5F97FED8A569E && gpg --export
--armor 31A5F97FED8A569E | sudo apt-key add -

gpg --keyserver subkeys.pgp.net --recv A278DF5EE8BDA4E3 && gpg --export 
--armor A278DF5EE8BDA4E3 | sudo apt-key add -

gpg --keyserver subkeys.pgp.net --recv F653CB3098D3F7A7 && gpg --export 
--armor F653CB3098D3F7A7 | sudo apt-key add -

gpg --keyserver subkeys.pgp.net --recv 580E2519969F3F57 && gpg --export 
--armor 580E2519969F3F57 | sudo apt-key add -

wget http://seerofsouls.com/keys/hawkwind.asc 
sudo apt-key add hawkwind.asc
wget http://seerofsouls.com/keys/philip.asc
sudo apt-key add philip.asc