Revenge Dramas:
Voice (2017)
Time Between Dog and Wolf (2007) Despite its year this one's really good
The Master of Revenge (2016)
The Bridal Mask (2012)
Secret (2013)
Birth of a Beauty (2014)
Romantic Doctor, Teacher Kim (2016)
City Hunter (2011)
Defendant (2017)
Sad Dramas (just search for dramas that are melo lol, and all of the above are actually sad):
49 Days
That Winter, The Wind Blows
Aogeba Toutoshi (japanese, very sad)
Super Daddy Yeol
Queen In Hyun's Man
Cruel City
Falling for Innocence
Mask
Gu Family Book
It's Okay, That's Love