The live recording of Rush's song "YYZ" that features Neil Peart's drum solo was solely responsible for causing my addiction to Rush a few years ago... and it's still a strong addiction hehe. So far I've purchased 19 Rush albums: all the studio albums and even one twice! I guess this also pretty much started me on the path that I am taking currently; it seems as though all the music I listen to and like now has somehow been influenced from Rush (it's kind of a strecth but maybe you get what I mean).
Also, Rhapsody's song "Emerald Sword" completely introduced me to the world of what I call Neo-Classical Metal and intrusmental metal. This has lead to me discovering artists such as Dragonforce, Rhapsody, Dream Theater, Liquid Tension Experiment, Warmen, Yngwie Malmsteen, Nightwish, and more. So far I've purchased all 3 of Dragonforce's albums, two of Rhapsody's albums, one Malmsteen, and two of Dream Theater's albums. This is easily in my top three genres, and sometimes it seems like it's me favorite.
I can't really recall any other life-changing songs for the other genres that I listen too such as jazz, classical, IDM, and others. I guess I have been listening to jazz and classical for almost as long as I can remember so that makes it hard to single anything out. If I had to guess I'd say for jazz it was Miles Davis and Maynard Ferguson since I play(ed) trumpet throughout school. And for IDM/electronic I supposed it might have been Aphex Twin's "Girl/Boy Song". Other than that I can recall listening to Mozart when I was quite a bit younger as well (maybe around 12 years old), so I guess I like music that has classical influences.