I can't think of *any* one song that I'd want to hear exclusively for the rest of my life.
Stairway is definitely one of the most epic, but if I had to pick just one it would probably be "Moving In Stereo" by The Cars. I've just always dug that song for some reason (yes, even before Fast Times At Ridgemont High came out!)
I can definitely think of a few others that would be "desert island" songs - but maybe that would be another good thread to start!