These are my favorites:
- http://reverie-context.livejournal.com/42728.html
- http://eunseung8693.livejournal.com/2970.html#cutid1 and its sequel : http://eunseung8693.livejournal.com/3440.html?view=22384#t22384
- http://kanae-mizuhito.livejournal.com/37436.html and its 2nd part: http://kanae-mizuhito.livejournal.com/37737.html?view=531561#t531561

suju-het.livejournal.com also has plenty well-written yoonhae fic. Just search on the tag 'yoonhae'.