For an example The Bridal Mask & The Equator Man. 
I would like if the relationship plays an important role in the drama (and both characters are mains). There can be 2 of them or more, I don't care. But I would like if the other one has at least little bit (more the better) antagonistic role. 
I don't mind hot actors either. 
Thanks for answers :D 

Cain and Abel
East of Eden
Triangle
Swallow the Sun
Athena Goddess of War
Punch
Hong Gil Dong
 
Warrior Baek Dong Soo

Thank you both. :) 
Lights and Shadows. Dunno if you would like the genre....but definite conflict between male leads
Friends Our Legend
The Devil
Cruel City (between Safari and Doc's Son)
The Chaser
For jdramas there're Double Face (adapted from the famous HK's movie Infernal Affairs), Karamazov no Kyoudai, Lady Joker