Haven't been posting here lately but this is too good to miss. There are lots of people who have technically great voices but there are far fewer who know how to sing. Technical perfection is a skill, singing is an art! As far as artists who are great singers but don't have a golden voice:
John Prine
Towns Van Zant
Kris Kristofferson
Lucinda Williams
Janis Joplin
Dylan of course
Cyndi Lauper
Warren Zevon
Guy Clark
You'll notice one common thread besides my musical taste...they are all great songwriters, so maybe they know how to communicate the emotion and the essence of their songs because it comes from deep inside them. Of course that's not to say that there are not great singers with golden voices who are not songwriters. Linda Ronstadt and Eva Cassidy come to mind, immediately