Love Triangle? Ok. I have a few, although some have been mentioned before.
My Girl - Hero, heroine and the hero's ex.
Sassy Girl Chung Hyang - This one is more like a square.
Coffee Prince - Erm... the love triangle is not that dragging so few last episodes are more focus on the hero n heroine.
Secret Garden - well, the conflict is more on rich vs poor but still have the love triangle issue a lil bit
Sungkyungkwan Scandal - A bit historical. But you wont really notice it. Sooo funny!
Full House - The love triangle here is heavy.
Goong - Same here. Heavy love triangle.
My Lovely Sam soon - funny. and you cant help but to feel sorry for the 3rd wheel.
Lie to me - Eun Hye just know how to cry.
The heirs - Kinda kids stuff. But still entertaining.
I think that's all i have for now.