After Grooveshark, another music scope is available for the Unity Music lens: Spotify scope.
The new scope lets you search for songs and albums from the Unity Music lens and play them in Spotify and in my test, it only worked using the native Spotify Linux client.
To install Spotify Scope for Unity Music lens in Ubuntu 11.10 or 12.04, use the following commands in a terminal:
sudo add-apt-repository ppa:scopes-packagers/ppa sudo apt-get update sudo apt-get install unity-scope-spotify
Then log out and log back in.
And as usual, remember to report any bugs you may find @ Launchpad with (for this scope, add "[spotify]" at the beginning of your report title).