For me it was Mai HIME, i was... 14? dunno, i've always liked anime and such but i didn't watch it frequently. So i had this friend that introduced me to Mai HIME, then saw that ShizNat blurry kiss scene and it began. I remember i was addicted to yuri fanfictions (in spanish, that's my first language...) wich included Shizuru x Natsuki, Mai x Mikoto and Kim x Shego (from Kim Possible, lol, deviantart had lots of good stuff from that series).
Then i had this long pause (about 2 years, maybe) from seeing anything with feels 'cause broken heart and silly stuff, but about 2 years or so i began to look out for yuri manga in spanish, then i tried in english (which is good for me to practice it, lol) and came to know dynasty.
I see begining with Kannazuki, Strawberry Panic!, Marimite and Girl Friends is common, i have to admit due to various reasons i have never watched the three first works, and i don't think i'm losing much /: dunno, really