i used to use tomahawk as a client for spotify but now like every other clients it wants premium membership to spotify, ace player though plugins to grooveshark and last.fm and loads of other sources. 
the website is here or just add the PPA to your apt sources. The different PPA are here select your distro apt get update and apt-get upgrade and then install, apt-get install tomahawk
https://launchpad.net/~tomahawk/+archive/ubuntu/ppa
to install the spotify client that will play without premium do this from a terminal.
sudo apt-add-repository -y "deb http://repository.spotify.com stable non-free" && sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 94558F59 && sudo apt-get update -qq && sudo apt-get install spotify-client
then the libcrypt fix as it doesnt just install straight out of the box on ubuntu 15.04
wget http://security.debian.org/debian-security/pool/updates/main/libg/libgcrypt11/libgcrypt11_1.5.0-5+deb7u3_amd64.deb
sudo dpkg -i libgcrypt11_1.5.0-5+deb7u3_amd64.deb