This is the one you want!

This app logs into Spotify on its own, so there’s no need to even have the Spotify app open on your Mac. It lives in the menubar and not only is it a deft controller, but it also allows you to (1) SEARCH for songs; (2) ADD a song to any of your playlists; (3) BROWSE any of your playlists (song title only); and (4) adjust the streaming QUALITY to 320kbps. These features set it apart from the rest. Additionally, it displays the album artwork in the controller - and will also notify you in the Notification Center at the beginning of each song (with: artist, song, album and artwork). Well done!!

H. Krinkle about Play for Spotify