Mac: One of the nicer features in iTunes is the MiniPlayer that shrinks the interface down and out of the way. MiniPlayer for Mac adds a similar function to Spotify and Rdio.
Based on the iOS jailbreak app of the same name, MiniPlayer for the Mac simply gives you a bite-sized controller for your music. You can set it up to work with iTunes, Rdio or Spotify. From the app, you can skip songs, search for tracks or share them.
If you're a fan of the iTunes MiniPlayer and want to use it elsewhere, this app does the trick.