Ji Sung and Hwang Jung Eum in Kill Me, Heal Me.
I second Barbie Hsu and Ariel Lin! Also adding Joe Chen, Ruby Lin, and Ady An. This is why they're Taiwan's leading actresses whose careers have already shifted to China! For the men, Jerry Yan, Chris Wu,  and Eddie Peng are the ones I can think of so far! 

Yoo Seung Ho!! in Missing You as Harry Borrison HE DEFINITELY WINS ALL THE WAY
Every time I saw him crying in that drama I wanted to kill whoever made him cry I felt I want to protect him by all means (no actor has managed to make me feel this way).



Park Bo Young, her crying just makes me wanna cry too! THIS FEELS!! EMOTIONS!!! T_T
I agree with Park Bo Young and Yoo Seung Ho, they make me cry right along with them.
Definitly Lee Bo Young in God's Gift - 14 days. Her acting was just awesome. I really thought, that she really lost her child. 
I love this thread.. In the male lead: I vote for Jung Kyung Ho in the cruel city.. Its not because He's my favorite actor but you are a rock if you didnt feel when he cry in the last episode(ps.I prefer if he cry to the shoulder of soo min.hehe)) u can feel that he's really really hurt..

In actress ; i will vote for Choi Ji Wo in Winter Sonata and Stairway to heaven... :)
Jo In Sung in It's Okay It's Love just killed me. 
And Ji Sung in KMHM
Park Bo Gum in I Remember You
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Lee Jong Suk in Pinocchio
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Yoo Seung Ho in Remember
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Gong Hyo Jin and Lee Joon Gi!
Kim Soo Hyun and Gong Hyo Jin
Lee wan
park yong- ha

Best two ,for me- Kim Soo Hyun and Gong Hyo Jin
runners up- Jo In Sung and Song Hye Kyo