My first rock record was The Beatles 1966-1970. I was already out of college by the time I bought this. To this day they're one of only two rock (as opposed to folk-rock) bands I have a serious collection of. Rod Stewart does absolutely zero for me; I once listened several times through a compilation tape a friend sent me, to confirm this.

I had a college roommate with a (then)-complete collection of Steeleye Span, so that's how I discovered folk (electric or otherwise). I don't remember what my own first purchase was, but Steeleye remains my favorite.

Fairport is good too, and Angel Delight may be my favorite of their albums.