It can be for various reasons. Maybe they will encourage someone to pick up an instrument, to open up to a new genre of music, to be more sensible to certain musicians etc.

There are lots I could post but I would get annoyed at not remembering every one of them so I'm going to post the ones I've listened to recently. Also I won't put YouTube tags because they make the page gigantic.

I also tried avoiding the songs that everyone already has listened to but it's hard to judge.

Miles Davis - Blue in Green
http://www.youtube.com/watch?v=PoPL7BExSQU

Pink Floyd - Comfortably numb (at the Pulse tour)
http://www.youtube.com/watch?v=JWnapx502uQ

Paco de Lucia - Entre dos Aguas
http://www.youtube.com/watch?v=0o8vszqVL2U

Silvio Rodriguez - Esto no es una elegэa
http://www.youtube.com/watch?v=zUwpbHyFyjg

Buckethead- Soothsayer
http://www.youtube.com/watch?v=adV8-_hgL4g

The Dead Kennedys - Holiday in Cambodia
http://www.youtube.com/watch?v=-KTsXHXMkJA

The Smiths - Please, please, please, let me get what I want
http://www.youtube.com/watch?v=DMQbzLrvwlE

Led Zeppelin - Since I've Been Loving You
http://www.youtube.com/watch?v=Bkjv9SscotY

The Pillows - Stalker
http://www.youtube.com/watch?v=Q3eOVCCkXU4

Jimi Hendrix - 1983 (A merman I should turn to be)
http://www.youtube.com/watch?v=SmRoGtiJp_E