Choi Min Shik - I would go as far as saying that he is the best actor in korean movies. He really goes into the roles that he takes on and makes it hard to remember that he is just an actor and not a gangster or a general. He is acting in a lot of the korean cult movies like Old Boy, Nameless Gangster, The Admiral, Tae Guk Gi and I Saw The Devil. Its not a coincidence that they were the ones that got to superstar status, Choi Min Shik is just that good.
Jung Hae In - He has made some great dramas although he hasn't really been noticed by the public until recently when he acted as the reliable policeman in While You Were Sleeping. But what made me put him on this list is his work in the drama Pretty Noona Buys Me Food/ Something in the Rain. He made one of the most convincing acts in a romantic k-drama in the history of dramas. Whenever he was on screen you really couldn't see whether he was an actor or a real person filmed in a real scenario. He felt connected to his role at a level that is beyond a "newcomer" to the game and delivered an emotional and real performance that brought me to tears at times.
Yoo Oh Sung - Can deliver so much emotion which you can see in his movies. Not as good on the smallscreen, feels like he got typecast as the scary father or gangster like the one he plays in Friend :/ Hope he gets over it because he is great as a lot of different types of roles
Yo Ah In - Versatile and a convincing actor that seem to work just as good on the small screen as in the big shot movies. His work in Six Flying Dragons, Veteran, Chicago Typewriter and Burning shows that he can take on any role.
Im Joo Hwan - Skilled supporting actor that has worked up to the big dramas and movies. He is perfect as the nice brother, fiance or boss, with nice looks and a great delivery, but that is not all; He also is perfect for roles as the antagonist! I think that he could become one of the top actors in a few years if he continues his acting like this.
Jo Jae Yun - My favorite actor, he isn't the best or most popular but he is so skilled. He has taken a lot of different roles during his career, he can play everything from the concerned husband to a scary sociopathic priest. His best works according to me would be in the thriller Save Me or his more playful role in Mad Dog.
Kim Woo Bin - Not really that good YET, but I believe that he will become the next Won Bin/Hyun Bin. He has the looks and is the amount of charm that you can't seem to hate him even if he plays a character that is beyond slimy like the ones he did in The Heirs and Twenty. His acting works in action, drama and comedy, and because of this he continues to show his own color through every role he gets no matter how different they are. He is funny and can show some tears when needed; What more can you ask?
Lee Jun Ho - An actor that I was surprised not to see at lists in the forum. He has showed that he can play complex and difficult roles with his work in Memory and in Just Between Lovers. He can't just take on serious roles, comedy is also a common genre that he works in. His acting in Chief Kim, Twenty shows that he is capable of choosing roles that has different characteristics and doing it with ease; Humor or Melo, Lee Jun Ho works in all scenarios.