ZOMG SPOILERS! If you've not played Valve's Portal, don't watch this video. It won't make any sense to you, and it might actually ruin the ending. Anyway, Jonathan Coulton created this song for the game and now a video of him preforming it live has surfaced on the YouTubes. I find it hard to overstate my satisfaction.
Give it a whirl if you care to, his other work is great too.
Jonathan Coulton sings 'Still Alive' [via Joystiq]