Probably Celis White back in the mid 90's. Started trying lots of different beers after that. A few others from that period that I remember sparking my love of beer (not just drinking) are Fuller's Porter, Chimay red, and most especially my first cask conditioned Fuller's ESB. After years of leaning heavily towards British and Belgian stuff and eschewing IPAs and other bitter nonsense I kind of got stuck with a 512 IPA at a bar in Austin one night and absolutely loved it. I've only in the past 4 or 5 months ever had any sour beers and I'm compelled to try them whenever I see them now. I've been drinking what I think of as good beer for almost 20 years now (legally) and am learning and appreciating more every day it seems.
P.S. I miss Pete's too.