Oh man, I've watched so many! I love My Girlfriend is a Gumiho. It's one of my favorites! I love Answer Me 1997 and BOF as well. Those are my top two. I'm in the process of watching The Heirs right now, and I just finished Flower Boy Next Door. I'd make a list of all the ones I've watched...but it would be so long haha. I'm kind of obsessed with them...
Oh and my favorite show (even though it's not considered a drama) is Running Man. I think that's the best show in the history of ever hahaha~