SPOILERS BELOW:
This is the credits song for Portal 2:
http://www.youtube.com/watch?v=Y9dA_OXyfU0
Not nearly as good as Still Alive IMO, but a fun song, haha.
Oh, the link still shows. Oh well.
EDIT: Fuck, I just watched a little Portal 2 co-op gameplay and someone spoiled the ending in the comments. I hope I don't remember it in a few months because I'm pretty sure I'll get this later.