Richard and Linda Thompson's 'Withered and Died'. Maybe not the happiest of songs, but certainly one of the most beautiful.
http://youtube.com/watch?v=kcKyZEnPWBQ
Ditto this absolutely amazing performance of 'A Heart Needs a Home' from 1975.
Warning: this song can radically change your life.
http://youtube.com/watch?v=xGhhAcjA-Ks