I'd say Duran Duran is the band that best defines the 80's, at least the stuff most people think of when they think of the music from that decade. For a single song, I can only give the nod to A Flock of Seagulls with I Ran.

I know there was more stuff in the 80's than the pop scene, but hair bands always seem to me to have started in the late 70's and pushed a little into the 90's, so I don't identify them with the specific decade as much.