I was looking for a way to download Songbird but the development for the Linux version has ended because of funding problems.
I tried to search for the sources packages but they have been removed from the internet and the songbirdnest.com development site is taken offline. This is probably the last stable version to be found on the internet and i hope that GetDeb will keep Songbird in their programs list.
To install Songbird you first need to download and install the GetDeb package, to download the package click on the link bellow.
When downloaded you can install the package using the Ubuntu Software Center (double click the downloaded file) or you can install it using the terminal window. To install the package using the terminal window press Ctrl+Alt+T to open a terminal window and copy+paste the following lines:
cd ~/Downloads/
sudo dpkg -i getdeb-repository_0.1-1~getdeb1_all.deb
When the package is installed you can install Songbird using the following command line:
sudo apt-get update && sudo apt-get install songbird
When the installation is finished you can close the terminal window and to start Songbird press the SuperKey and type: songbird