Both Dong Yi and Queen Seondeok are great. In Dong Yi, I liked the chemistry between the main pair, they are cute and funny. Queen Seondeok is really epic and I do think Mishil and Bidam really made the drama shine.
Lol I came here for drama recommendations but I already have most of the titles here watched or PTW-ed xD
My recommendations!
K-dramas: I also really liked Queen Seondeok.
Jumong
And one does not simply forget the classic Jewel in the Palace, how has no one mentioned it - or has everyone watched it already?
HK dramas:
Rosy Business
Beyond the Realm of Conscience
Sweetness in the Salt
And then there's also My Fair Princess, also another classic :)