The first song I remember listening to was Keep Fishing, although the first time I remember hearing Island In The Sun, it sounded slightly familiar, so it's one of those two.
I'm quite sure it was Buddy Holly. It was all over the radio when I was 14 I'd think. Didn't get into Weezer until 7 years later with Green Album. Kinda ashamed to say this :P
El Scorcho was the first song I heard and owned on a compilation on MTV's "Alternative Nation"