Simon & Garfunkel
Peter Paul and Mary
Kick-ass HARMONY! I often describe myself as a lazy musician, but I have a pretty good ear. I can sit and listen to a piece of music and create harmony in my head. I don't know how I can do it (I have not had a lot of formal music training)--it just comes to me. So I get the art part...but wouldn't be able to explain to you the mechanics of how to do it.
But...Girlyman, one of my all-time favorite bands (with kick-ass harmony--I describe them as a cross between Peter Paul and Mary and the Indigo Girls) have made a video featured on Slate.com explaining how to make harmony. Check it out (if you are reading this directly on my blog, you might want to mute the piped-in music by going to "Some of My Favorite Music" on the right nav bar):
I never get tired of listening to those gorgeous harmonies!