Title. So far I've watched Iljimae, City Hunter and currently watching The Bridal Mask, all 3 of them are awesome and I want more! Not interested in Return of the Iljimae, is there anything else out there? Right, it has to be Korean.
Hong Gil Dong was a secret hero at the beginning but it soon became well known who he is.
Unfortunately you have it on your completed list so that's an invalid recommendation.

I skimmed through my completed list and I don't have any other drama to recommend but on my plan to watch list there are two historical hero dramas that I want to watch; The Legend, Warrior Baek Dong Soo, but I'm not sure if the hero has secret identity.
Sorry I couldn't be of much help.
Jeon Woo Chi but he doesn't have a mask or anything; only that people hear about his deeds without seeing him.
Not a drama, but a movie - The Man from Nowhere
Myung Wol the Spy, I liked the 10 first episodes but then it was kinda draggy.
Cruel City for now? (i haven't watched the next few episodes yet so.....) Time Between Dog and Wolf - Double Agent w/ conflicting identity/loyalty. Trust me, this one's real good!
there is one called Sweet Spy and then there is Bad Guy...but he isn't a hero...he's a secret bad guy.
goldenseal50 wrote: there is one called Sweet Spy and then there is Bad Guy...but he isn't a hero...he's a secret bad guy.


I've always wanted to watch Bad Guy....but never got the courage to b/c i read the ending wtf spoiler.
phoenixbasilisk wrote: I've always wanted to watch Bad Guy....but never got the courage to b/c i read the ending wtf spoiler.


Me too, I guess it's pointless now..
Just wanted to point out that for some of these suggestions (Healer, The Man from Nowhere - the rest I haven't seen myself so I don't know), the main character is not a hero in the sense that he's an all good, ideal, moral, brave protagonist. They really do make some morally questionable choices :P
But since you wanted something similar to City Hunter, I guess that's not the definition you implied anyway? In that case I really second Healer it's a great drama and Ji Chang Wook is awesome in there!