Pass! They would make a good on screen couple although I'm a bit worried about their height since both are 176cm tall. Sung Kyung might appear taller with some heels.

Yoo Seung Ho and Kim Yoo Jung
Pass. They are both veryy good looking plus the age gap is not too huge.

Kim Jihoon and Jung Eunji
Fail... I don't really see it.

Ji Chang Wook and Nam Ji Hyun
Pass! We already get to see that strong chemistry ^^

Seo Kang Joon and Park Min Young
Pass! It seems a good couple.

Ren Wei & Yan Jerry (chinese)
Fail

Kim Young Kwang and Park Bo Young
Fail 

Choi Jin Hyuk and Ha Ji Won 
Fail, I do not like Ha Ji Won

Kim Jae Joong and Uee
I knew they'd be together in a new drama and i really hope that they have chemistry, but i can't imagine them as a couple for now. So, fail.

Kang Chul Woong & Kim So Eun
Fail (Sorry I do not know Kang Chul Woong and haven't seen him in any dramas)

Lee Won Geun and Joy (Red Velvet)
Fail, I do not like idols

Shin Dong Wook and Seo Hyun-jin
Pass. It sounds good.

Na Hae Ryung & Park Eun Seok
Pass. I like them

Lee Min Ho & Yoon Eun Hye
Fail. It's weird but I find it hard to see any chemistry between Lee Min Ho and other female actresses.

Park Shin Hye and Ji Chang Wook
Fail, I do not like Park Shin Hye

Shin Dong Wook and BoA