Don't get me wrong, Spotify's music collection is already pretty darn huge, but it would be great to see you guys reach out and support many more local, and overlooked bands. There are plenty of artists that cannot be found, or only have a limited selection of songs from on the catalog. PLEASE PLEASE PLEASE, try and obtain more independent artists. Also, for hip-hop music, it would be incredible if you could somehow acquire rap artist's recent mixtapes. For instance, Frank Ocean, Nostalgia/Ultra, would be a great addition to Spotify, and many other mixtapes. And, lastly, maybe a indie spotlight, which lists a few pages of recommended independent artists that are coming up. If not that, give the album recommendations a little revamp, by giving a whole section dedicated to it on the sidebar, sort of like Rdio and Mog, showing the user a list of albums that they might enjoy.
Also, maybe some more music from other countries, like some Austrailian music. The radio station in Australia called Triple J supports a lot of incredibly talented bands. Reach out to some of those sites, and try and get deals with bands on there?