Incase there is no BigBoss repository present in Cydia after you jailbreaked your iDevice with Sn0wbreeze, PwnageTool or Redsn0w then here is a simple way to add it. All you need is a jailbroken iPhone, iPod Touch or iPad with OpenSSH installed so that you can SSH into your iDevice using WinSCP (Windows) or CyberDuck (Mac).

Add BigBoss Repository to Cydia via SSH

1. Open Cydia, search for OpenSSH and install it on your iDevice.
2. Download bigboss.list file from here and jump to step 5. Alternatively you can use the steps below to create bigboss.list file manually.
3. Open Notepad in Windows. If you are on Mac, open TextEdit and copy-paste the following code into it:

# do not edit this file to add your own custom sources
# this file is subject to be upgraded as part of a package
# either add your own .list file to /etc/apt/sources.list.d
# or add your entry to the global /etc/apt/sources.list file

deb http://apt.thebigboss.org/repofiles/cydia/ stable main

4. Go to File menu, choose Save As... and name the file "bigboss.list" (including quotes)
5. SSH into your iDevice using WinSCP, CyberDuck or DiskAid, navigate to root->private->etc->apt and place bigboss.list file in sources.list.d directory
6. Thats it. Reboot your device and you are done!

Update#1: Now you can use iPhone Explorer to put bigboss.list file in sources.list.d directory without SSH.
Update#2: Add ModMyi or BigBoss Repo to Cydia directly from Saurik repo. Read details here.
Update #3: Top Cydia Sources