Some of (what I think are) the hidden gems of TV.

Luther

Let me start off by saying I have a MASSIVE man-crush on Idris Elba. I think his acting is consistent in everything and I just love him. Luther brings on a darker side to your typical crime-show - John Luther constantly battles both himself and others in order to live his own life, but along the way is forced to struggle with the consequences of his previous actions. This makes for some interesting decisions on his part, and makes for a thrilling watch. (Be warned - the show is rather gruesome at times, so make sure you've got a thick stomach before watching!) What I love most about Luther is the constant edginess of it - everything is wont to change within a matter of seconds, and as well as this, it's not your typical "whodunnit" - from the offset, you know who the criminal is, and this allows for a greater connection to the show in my eyes. Honestly, I can't recommend Luther enough.
3 Seasons, 14 Episodes total.

In The Flesh

Now, In The Flesh is slowly gaining popularity but unfortunately there is a chance that there might not be a Season 3 due to the poor viewing figures for Season 2 (do not let this disconcert you). In The Flesh is again, not a typical show for its genre. Rather than focus on the survivors of a zombie apocalypse, it focuses on the cured undead, or "partially deceased syndrome sufferers" as they try to rejoin the society which they helped destroy. It's a show that truly makes you think, and it's engaging all the way through, as well as amusing at times.
2 Seasons, 9 Episodes total.

Orphan Black

I'm not too sure if Orphan Black is as unheard of as I think it is, but I know it's actually pretty popular, and I think it should achieve cult-hit status. Orphan Black follows the life of Sarah Manning, a small time street hustler whose life is completely changed when she witnesses the suicide of a girl who looks just like herself. She quickly assumes her identity, but as things go on, nothing is as it seems. The show explores the ethical issues of cloning in a thought-provoking manner, all the while retaining an element of humour, but stays disturbing enough at times to truly creep you out. Tatiana Maslany performs perfectly in it, and I think this show deserves way more attention.
2 Seasons, 20 Episodes total.

Blackout

Starring Christopher Eccleston (who is absolutely fantastic), Blackout looks at Daniel Demoys, a councilman who gradually becomes disillusioned with life, but after taking a bullet for someone, he gains popularity to the extent that he runs for mayor. Throughout this, he must try his hardest to bury his own secrets, which could end up destroying him. It also features Andrew Scott (Moriarty in Sherlock) who is just great in this, and really plays his role perfectly.
This and Exile were only three-show series, and thus have remained relatively hidden, but I still love them.
1 Series, 3 Episodes total.

Exile

John Simm stars as Tom Ronstadt who visits his father, only to uncover a shocking revelation about himself, his family, and the life he thought he knew. It runs as a Father-Son story, but it has elements of a psychological thriller to it, as Tom explores a hidden past that should never have happened. Exile truly is one of the most thought-provoking shows I've watched, and when it ends, it actually haunts you (or at least it did me). Perfect acting, and a well thought story make this a very interesting watch indeed.
1 Series, 3 Episodes total.