Jan Kraus: Sherlock, Jekyll, The Crimson Petal and the White and Spartacus (both are a quite explicit), Game of Thrones, Napleon Dynamite (if you've seen the movie), Californication (great for cultural refferences), American Horror Story (for horror movie lovers), Breaking Bad, Dexter, Uk version of Shameless, Community.
And my personal favourite Avatar: The Last Airbender – has well written dialogues, each character is complex you get to admire even villains, great jokes. Storyline is well structured and the series is finished with an amazing finale. The whole show has very few filler episodes and there is only one episode I don't enjoy very much. And trust me, I am very critical and hard to please.