This is exactly how it says on Spotify's homepage

Music catalogue updated with 21,060 tracks
September 23, 2009, 11:33

Another music update today. We added 1,673 albums and singles to the catalogue, in total 21,060 new tracks are now available.

A few highlights include:

* Tomhet, Idel Tomhet by [ingenting]
* A number of releases from speed metal band Stormwarrior

Have a look at the Google doc for the full listing of all the releases. As with every update not all albums listed may be available in your country and some tracks previously available may no longer be playable due to regional restrictions.

Let us know what gems you find in this update.