Mine was "To the Beautiful You" :)
You're Beautiful was mine. (Though technically I watched Cinderella's Sister, but things didn't work out for me.)
The first one I ever tried was Coffee Prince and I made it through one episode before turning it off. The one that really got me into the genre though when I gave it all a second chance was Shut Up: Flower Boy Band

mine was sorry i love you,,,
it was great drama and i miss the main lady since she do movie now

Mine was Playful Kiss! I was into anime and watched Itazura Na Kiss, then found out about a live action version (kdrama)! The music on the show also got me into Kpop. And thus began the obsession. 
"Lovers" <3 I'm gonna rewatch it in the future, but I really doubt that after seeing other great dramas it'll be as good as it was...
Mine was 49 days, but I only started watching Korean dramas because I had seen bits and pieces of one when I was travelling in Vietnam and even though I didn't really know what was going on since it was in Korean subbed in Vietnamese (neither of which I knew at all) it completely sucked me in and I decided to try watching Korean dramas (that drama ended up being Boys over Flowers, which was the second one I watched, typical, haha).
Boys Over Flowers for me..
Mine was a mix- I started watching Heirs during its season, in between new episodes I started Boys Over Flowers (b/c Lee Minho)  and was hooked before either was over LOL.

Mine was Stairway to Heaven. I watched it with my granny, loved it so much!

Mine was Personal Taste.

I was watching Hanazakari no Kimitachi e on veoh.com (a long time ago) and I missclicked and saw this.
I first thought: dafuq is this shit, but I completed it before completing the HanaKimi one.