My life changed when I first heard "Walk on the Wild Side" by Lou Reed. It sparked an interest in classic rock that has informed my taste in music to this day.
Guns n Roses, Metallica, and Van Halen (their early stuff, with David Lee Roth) probably deserve joint credit in getting me interested in heavy rock music. Van Halen more than the others I guess because I heard them first, but GnR and Metallica deserve mentioning because they were the first hard rock/metal groups I ever really got into.
Without The Clash's London Calling I may never have gotten over my opinion of punk music as nothing more than repetitive and amateurish; I now consider it my favorite genre of music. Moby's Play led to a similar epiphany regarding the merits of electronic music.