If your talking modern music then I would say something by Elvis. Probably Jailhouse Rock. Almost every genre of modern music can trace its roots back to Elvis. Most of what I see people listing are songs that are trend setters for a particular genre but not important in a broad sense.

Looking on line I found that there are about 1000 different opinions on this subject though. One link had a David Hasselhof song in the top 10 most influential of all time.