Ji Soo
So Ji Sub
Lee Joon Gi
Lee Min Ho
Park Shin Hye
Ji Chang Wook
Park Bo Gum, Jung Kyung Ho, Ji Sung, Lee Jong Suk, Ji Chang Wook, Song Joong Ki, Byun Yo Han
Kim Min Jong
Jang Hyuk
Bae Yong Joon 
Gong Yoo
etc.... check my profile n u'll know haha http://mydramalist.com/profile/YmsKmjKn 

Right now
Gong Yoo
Lee Dong Wook
and Sung Jae
:D
I have too many favorites! I'll narrow it down to three or else the list will be too long. 

Jung Kyung Ho 
Park Bo Gum 
Lee Dong Wook 

Gong yoo
Lee dong wook
Lee jong suk
Sung jae currently all this.
All time favourite: Yoon Seung Ho! And also Chan Jackie :)
Jung Kyung Ho
Lee Seung Ki
Yoon Shi Yoon
Seo In Guk
Kim Woo Bin
Park Bo Gum
Lee Hong Ki
Ji Sung
Ji Soo
So Ji Sub
Yoo Ah In
Jung Woo Sung
Kim Soo Hyun
Ji Chang Wook
Nam Gung Min
Ji Sung
Nam Joo Hyuk
Park Seo Joon
Ji Soo
Favorite:
1. Jung Kyung Ho--My Doctors Son
2. Kim Nam Gil-My beloved BIDAM!! :)
3. Jang Hyuk-well all his drama was love.. :)
1. Kim So Hyun
2. Yook Sungjae
3. Choi Minho
Kim Jae Wook, Won Bin, Joo Won, Gong Yoo, Hyun Bin, Lee Dong Wook 
Seo In Guk. I love him in Shopping King Louie, he is so cute and stupid. He is the most handsome guy on the planet. People say he is not that good!?!  Also Sungjae, i love him! 

Jeon Ji Hyeon, Lee Jong Suk, So Ji Sub, Gong Yoo, Shin Min Ah and Dong Wook. But there are really many talented korean actors. 
Park boyoung, Shin se hui, lee sung kyung, kim yoo jung, park hyung sik