Once Valve heard about the project, they authorized GLaDOS voice actor, Ellen McLain, to produce the custom audio track for the level.
The result is pretty awesome.
It amazes me that people still question what the best game development company is.
... And for no other reason than I love this song, here's the video for 'Still Alive' from the end of Portal 1.
Well, I'm off to replay the Portal games... again.