I loved the 'Iljimae' soundtrack, and I have a soft spot for the instrumental pieces in 'Tree of Heaven'. =]
Most OST on my playlist comes from : Boys Over Flowers, To the beautiful you, You're beautiful, Save the last dance from me & Mary stayed out all night. Though, i also like one or two songs from : Heartstrings, Secret Garden & Goong.
Protect The Boss, Boys Over Flowers, and We Got Married's Ssangchu Couple!
Snow Queen Goong I Do I Do (I like Her Over Flowers by Yesung. I love Yesung. ^-^
Personal taste Secret garden The moon that embraces the sun City hunter 49 days
49 days, boys over flowers. I think I have a lot more OST favourites from J-dramas lol...
Hm Sungkyunkwan Scandal, Cinderella's sister, Mary Stayed out All Night and Heartstrings had some of the best OST in my opinion :3

I want to say Rooftop prince and Missing you but I'll sound biased so I won't
The Moon That Embraces The Sun - Back In Time Love Rain - Because It's You Dream High - Dream High Queen In Hyun's Man - I'm Coming To See You To The Beautiful You - Stand Up To The Beautiful You - U You're Beautiful - Without Words
Mine favorites OST Star in MY Heart, all songs and music in this drama is just amazing. OST Rock, Rock, Rock, not only well known and classic rock music from west but from Boohwal and other korean rock legends too From other dramas its just parts of OSTs what i like - opening/ending or some song in the middle.
Shut Up Flower Boy Band OST <3333 Romance Town OST <3 City Hunter OST <333
Just to add since I saw 49 Days recently....all of the OSTs in that series were fantastic!!!! Collected them all :)
this is too old but i loved the (fate) from full house which was my 2nd drama dream high 2 : (B) was definitely something heartstring: ( i miss you ) is full with feelings, totally loved it gentleman's dignity : if you come into my heart , romantic classic and deep sexy voice
I'm loving the ost in Cheongdamdong Alice especially the songs from Baek Ah Yeon and K.Will
"Fox Rain" - My Girlfriend is a Gumiho (nine tailed fox) "Fool for you" - Padam, Padam... "My Heartache" - A Gentleman's Dignity "Goodbye Day" - Bridal Mask "You've fallen for me" - Heartstrings