Honestly there hasn't been one song that's made me listen to an artist. Usually i see someone getting great reviews and then i listen to the album to see if i'll like them. The Last time a song really caught my attention and made me ant to listen to someone was probably Lupe.
Quite a few but one that I'm listening right now is Cudi, Day and Night... I heard that shit in an episode of entourage and actually watched the credits to see who the fuck that was. That shit didn't sound like anything else out at the time.