The soundtrack for Portal is contained in the The Orange Box Original Soundtrack released on December 21, 2007. The soundtrack also contains tracks from Half-Life 2: Episode One and Two and Team Fortress 2.
The Orange Box Original Soundtrack can be purchased from Amazon and iTunes. The tracks from Portal can be found in .mp3 format inside the Portal game cache file (portal content.gcf) under the directory \portal\sound\music\.
Track listing
1. Subject Name Here - 1:44
2. Taste of Blood - 3:06
3. Android Hell - 3:45
4. Self Esteem Fund - 3:30
5. Procedural Jiggle Bone - 4:34
6. No Cake For You - 4:05
7. 4000 Degrees Kelvin - 1:01
8. Stop What You Are Doing - 4:00
9. Party Escort - 4:21
10. You Can't Escape, You Know - 6:24
11. You're Not a Good Person - 1:24
12. Still Alive - 3:05