drama with a secret relationship

Thats also one of my favourite troops :)

Some I can recommend:
korean Drama: 
Romance is a Bonus Book
Something in the Rain
I hear your voice
One Spring Night
Her Private Life
A Business Proposal
Crash Course Romance
Hometown Cha Cha Cha
Nevertheless
Search: WWW
What's Wrong With Secretary Kim
Where the Stars Land
My Secret Romance
Cunning Single Lady - here its a little tricky. This is a divorced couple that ends up working together. They keep their connection secret from their coworkers. So its not per say secretly dating but they do en up to some degree in that position. Truly a super well done drama.

Chinese/Taiwanese:
Dating in the Kitchen
Lost Romance
Before we get married 
Perfect & Casual
Vacation of Love - Omnibus drama, so lots of different couples that are all interlinked with one another and all a couple of them have a secret romance story line
Hello, Again!
Find Yourself
Somewhere only we know
Sweet teeth 

Japanese:
Siren
Konin Todoke ni Han wo Oshita dake desu ga
Shanai Marriage Honey