Testify is a native Linux Spotify client.
It uses the libspotify library that is available from the Spotify Developer web site. You will need a premium Spotify account to be able to use Testify.
You can download a pre-compiled version here. Then follow the instructions in the HOWTO-install file.
Please note that the code is still in development, but the binary releases should be stable.
svn checkout https://xtestify.svn.sourceforge.net/svnroot/xtestify/trunk testifyTo build your own Testify client from source you will need to request an Application Key from the Spotify Developer web site.
Then follow the instructions in the HOWTO-install file.