I recommend...
Mystery thrillers since these type of dramas always have a duo who work with each other so complemently and their friend ship is just to die for!
Signal
Life on Mars
Forest of Secrets
Children of lesser God
Pied piper
If you want romance in your recommendation where two characters fall in love with each other while helping each other, then...
Birth of a beauty(Male lead will really make you laugh your worries off)
Our times (This movie will make you think over so many good things you missed in life)
My name is Kim Sam soon(Why is that everytime I recommend someone this drama, I want to watch it over again!)