I have quite a few candidates for this, the biggest ones being:
Tori Amos, who I got into in the middle of the year, July or so, and since I started listening to her 4-5 months ago, she has gone from about 4-5 listens to 1,6k listens on lastfm.
I consider her to be one of my absolute favorite artists, and I have already picked up all of her studio albums (physically) with a few other ones as well.
Sigur Rós - Got into them very early this year, probably in January already, I remember it so clearly because I was playing a lot of World of Warcraft then, (it was right after Cataclysm was released, like 1 month in), and I listened to Sigur Rós like all the time I spent in that game at that period. Was really soothing and peaceful, some good memories of it.
I have over 1k plays with them on lastfm now as well, fairly decent in a year for me.
Two other candidates would be Pain of Salvation and The Dear Hunter, but I had already heard them some before, but those two really CLICKED for me this year, before I had sorta lukewarm/OK-ish feelings towards them, but they clicked bad, and are now very high up for me.