H.O.T. though.......
SHINee's Lucifer - I fell for Taemin in this, his hair was great ^^
I think It was B.A.P (One Shot) or SS501 (Deja Vu)
EXO... and I actually became interested in the group after watching Do Kyung Soo act in the movie Annoying Brother. I wanted to learn more about him since he was so great in the movie, and it just threw me into the K-pop universe. :) I'm fairly new here, but enjoying my time!
Bang bang bang by big bang which came up randomly on Spotify. I'm still very new to the kpop world. Lucifer, Sorry sorry and call me baby have become some of my favourites till date.
Super Junior - It's You 
snsd - genie  loving the girls to this day 
SHINee - Lucifer
Bless Youtube for recommending me these 5 boys.
my first kpop group is JYJ, i discovered it because of JaeJoong 
SS501 - Love Like this, A Song Calling For you

After I watched my 1st KDrama Boys over flowers, I wanted to know more about Kim Hyun Joong and got introduced to K-Pop..And I'm glad I did :)
The first Kpop group I discovered is B.A.P (it's still one of my favourite groups) and I remember having Miss A's Good Girl Bad Girl stuck in my head when I started listening to more Kpop :)