Portal 2 soundtrack

Songs to Test By is the soundtrack for Portal 2. Songs to Test By was made available free from the Portal 2 official website in .mp3 format, and a 4-disk Collectors Edition is available to purchase from Amazon.

Shorter versions of particular songs, or sound effects from the game, are available as ringtones from the website above. The soundtrack was released in three volumes: The first, titled Volume 1, was released on May 25, 2011; Volume 2 on July 1, 2011, Volume 3 on Sept. 30, 2011, and as a 4-disk Collectors Edition on October 30, 2012.

The Collectors Edition also includes in-game promotional items for Team Fortress 2, and to & in-game promotional items for Dota 2, and the Turret Lullaby comic.

Collectors Edition Disk #4
There are no downloads because it's a copyrighted disk.

Others
1. Exile Vilify - 4:46 by The National

Trivia

 * The track 9999999 is actually a remix of Music of the Spheres I, best heard when the slow part ends.
 * The track The Courtesy Call has its first part unique to itself, the second part is a sped-up version of Music of the Spheres I and the last part is a slowed-down version of Reconstructing More Science