Dark-ambient musician Zac Bentz (aka Dirty Knobs) recently released a remix of five tracks from the Portal 2 soundtrack, turning each track into 20+ minutes of dark, droning soundscapes. If you're a fan of dark-ambient music or Brian Eno-esque soundscapes, this is a must-listen.
The full album, Dream With Portals, (clocking in at over two hours) can be downloaded for free at his Bandcamp here. From there, you can also check out some of his other works, including his excellent Field Recordings From the Edge of Hell.
Put this album on tonight for dreams of stark white testing facilities, the hum of machinery, and the crushing solitude Chell and the Ratman must've felt throughout their time in the Aperture Science center.