The Raspbian repository is the entire set of Raspbian packages organized in a special on-line directory tree which can be used to install thousands of additional software packages on your Raspberry Pi.
The master Raspbian repository can be found at the following link:
Mirrors of the Raspbian repository that may be more suitable for users in different geographic locations can be found here.
Repository sources.list File
The /etc/apt/sources.list file contains the information needed to install additional software packages on your Raspberry Pi from the Raspbian repository. This file should contain the following information:
deb http://archive.raspbian.org/raspbian wheezy main contrib non-free deb-src http://archive.raspbian.org/raspbian wheezy main contrib non-free
If needed, the Raspbian public key can be stored into your apt-get keyring using the following command:
wget http://archive.raspbian.org/raspbian.public.key -O - | sudo apt-key add -
Bandwidth statistics of the Raspbian repository can be found here.