'Gypsy,' Fleetwood Mac
This 1982 song originally began as a Stevie Nicks solo effort about her early days with bandmate and former bed mate Lindsey Buckingham. But as her friend Robin Anderson became ill with leukemia, the line Nicks had included for her -- "I still see your bright eyes" -- became much more powerful, and Nicks saved the tune for Fleetwood Mac. Anderson died two days after giving birth to a baby boy.
http://www.spinner.com/2010/05/24/best-memorial-songs/