I'm a big fan of Once Upon a Time (available on Netflix).
It can be cheesy as hell, but it's a nice series to watch when you want something that's not too intensive, this like popcorn movies. Leave your brain at the door and just enjoy the series for what it is. Fairy tale characters brought into the modern world, but as always, with a twist.
I've heard good things about Sleepy Hollow, Grimm and Penny Dreadful, but I haven't had a chance to watch it myself. I'd like to hear peoples opinions on these, to see if they are worth getting into.
Also, there was a mini series on Sky Atlantic a while ago called Ascension. It was brilliant but it looks like it's not been picked up for any further development which is really sad