As reported at The Steam website, for $9.95:

Embark on a musical odyssey spanning the shades of the Orange! Featuring 19 original compositions, the official soundtrack to the Orange Box delivers troop-rallying anthems of Team Fortress 2; the rich, textural soundtracks of Half-Life 2: Episodes One and Two, and Portal's atmosphere, sometimes temperamental, electronica.

As a special bonus, the CD features two versions of Janathan Coulton's "Still Alive": the in-game mix featuring Ellen McLain as the voice of GlaDOS and Coulton's vocal mix, an exclusive track unavailable anywhere else.