From SubfireWiki

/etc/apt/sources.list

Posting good sources.lists is a good idea. However, EasyUbuntu can create a nice one for you at the click of a button (and install and enable a bunch of extra packages).

Dapper

deb http://us.archive.ubuntu.com/ubuntu dapper main restricted
deb-src http://us.archive.ubuntu.com/ubuntu dapper main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu dapper-updates main restricted
deb-src http://us.archive.ubuntu.com/ubuntu dapper-updates main restricted

## Uncomment the following two lines to add software from the 'universe'
## repository.
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## universe WILL NOT receive any review or updates from the Ubuntu security
## team.
deb http://us.archive.ubuntu.com/ubuntu dapper universe
deb-src http://us.archive.ubuntu.com/ubuntu dapper universe

deb http://security.ubuntu.com/ubuntu dapper-security main restricted
deb-src http://security.ubuntu.com/ubuntu dapper-security main restricted

deb http://security.ubuntu.com/ubuntu dapper-security universe
deb-src http://security.ubuntu.com/ubuntu dapper-security universe

deb http://archive.ubuntu.com/ubuntu dapper multiverse
deb-src http://archive.ubuntu.com/ubuntu dapper multiverse

Breezy

deb http://us.archive.ubuntu.com/ubuntu breezy main restricted
deb-src http://us.archive.ubuntu.com/ubuntu breezy main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu breezy-updates main restricted
deb-src http://us.archive.ubuntu.com/ubuntu breezy-updates main restricted

## Uncomment the following two lines to add software from the 'universe'
## repository.
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## universe WILL NOT receive any review or updates from the Ubuntu security
## team.
deb http://us.archive.ubuntu.com/ubuntu breezy universe
deb-src http://us.archive.ubuntu.com/ubuntu breezy universe

deb http://security.ubuntu.com/ubuntu breezy-security main restricted
deb-src http://security.ubuntu.com/ubuntu breezy-security main restricted

deb http://security.ubuntu.com/ubuntu breezy-security universe
deb-src http://security.ubuntu.com/ubuntu breezy-security universe

deb http://archive.ubuntu.com/ubuntu breezy multiverse
deb-src http://archive.ubuntu.com/ubuntu breezy multiverse