As it seems everyone already recommended Secret Garden. I will recommend Maou, Mr.Brain, Mukodono, My Boss My hero, Rolling Love, X-family (seeing it without watching K.O) aaand.... I forgot what was it called, but it was a 5episode drama with the DBSG band as main (if you like and know the band).
There's just so many to recommend.. So I will tell you the ones that I remember
Romance Town (I'm currently watching and it's funny and unexpected) Playful Kiss (No words to describe how perfect!) Heartstrings (If you watched You're beautiful and hoped that the main character would be with the second guy, than this drama is a MUST)
If you'd like abit of time travelling dramas, i would definitely recommend - roof top prince - Queen in hyun's man Some dramas that i've been following up recently - i miss you - Big - To the beautiful me - Arang and the magistrate - Faith Hope this is helpful :)