I've never played Portal, but this is still fucking hysterical.
Portal has a kick-ass closing-credits song. Where "Kick-ass" equals "bizarrely, surreally, absurdly literal" and "closing-credits song" equals "woulda been a J-pop love ballad."
You can see the closing credits on youtube.
The folks at VGCats did their own music video of the song,
Yes, it's one of those rare times when something that's patently absurd to start with is successfully made a bit more absurd.