Jonathan Coulton, nerd songster supreme, has posted about his experience writing the end theme to Portal, part of what might be the best videogame ending sequence ever created.
I recorded a version with some scratch vocals and we sent it to the voice actress who did that character in the game, Ellen McLain. We all went into the studio to record her vocals, then did all the fancy computer sound things they do to make her sound like a computer voice. Ellen's a classically trained soprano, and a very talented voice actress - she has this character down perfectly, and she did a great job conveying emotion in a non-emotional way. Between her and the very strong writing behind her character's dialog, it was hard for me to not end up looking good in all this.
He's posted both lyrics and chords, although no easy downloadable MP3 yet. (There are MP3s floating around though I've heard.)
Portal: The Skinny [JonathanCoulton.com] (Sorry about the missing link!)