Probably the most famous ad ever seen. I'd Like to Buy the World a Coke (1971).

I’d like to buy the world a home and furnish it with love,
Grow apple trees and honey bees, and snow white turtle doves.
I’d like to teach the world to sing in perfect harmony,
I’d like to buy the world a Coke and keep it company.
It’s the real thing, Coke is what the world wants today.

You can read the full story behind this commercial here: http://thisisnotadvertising.wordpress.com/2011/12/15/coca-cola-id-like-to-buy-the-world-a-coke-the-story-of-hilltop/

Advertising Agency: McCann-Erickson, USA
Creative Director: Bill Backer
Art Director: Harvey Gabor
Director: Roberto Malenotti
Agency Producer: Phil Messina
Music: Billy Davis, Roger Cook, Roger Greenaway, Bill Backer