Here's the wiki list of unofficial add-on repositories.
Code:
http://wiki.xbmc.org/index.php?title=Unofficial_add-on_repositories
To Instal a repository you will have to down load it and transfer it to a usb stick. The file is in zip format Do not unzip the file xbmc does that for you.
plug in the usb stick and allow it to initialize...
Open xbmc and go into systems/settings then select the add-ons tab.
Then select instal from zip and you will be prompted to find the file
It will be located in the root file system, when your there you will want to select mnt/sda1. It could read sda0-2 depending on what usb port your using.
Select the repository and click to instal.