I have a couple, as well as reasons...
Beethoven's Moonlight-My mom forced me into piano lessons, and I hated it...until I heard this. It gave me a real appreciation for the insturment, the way its played, the way its written....and its really, really beautiful.
Eric Clapton-Layla-I mean the real one with that AWESOME RIFF. I was 10 and buying crap pop recorRAB when I heard this.
Green Day-Redundant-Kind of blew my mind, because it expressed my exact feelings...I also love the composition, I don't care how commercial it is.
The Clash-London Calling-Non-biblical song about the appocolypse. Started my obsession with lyrics.
Black Flag-Depression-Started newfound appreciation for hardcore.