Northern magic has been boosted, but I doubt it was caused by the rebirth of dragons. Rather the rebirth of dragons seems to have been caused by the recent surge in magic, much like like northern magic in general. I would say the recent surge in magic could be attributed to several things, here are my top three:
The red comet. While it only became visible recently, we can assume it was drawing closer to the fire and ice world, and now that it is 'overhead' magic is at its strongest. Or, it too is the result of the surge in magic, though this seems unlikely.
Natural ebb and flow of this world. Magic rises and recedes and this is the way of things and always has been.
The Night's King. His rise could also have triggered the rise of magic, possibly to provide the means to resist him. The question here is, why didn't he rise sooner? If it is the same Night's King of legend, he has been around for a long time, so why now? If he is a new figure being mistaken for the Night's King, it begs the same question, why now? If he 'unleashed' or 'harnessed' some new power, I would think GRRM would have hinted at it by now. I thought about giving the Others their own category, but, although they seem to have somehow bestowed the Night's King's power on him, he appears to spearhead their advance. It's possible they have done something to open the flood gates of magic, but their absence from the shows and obscurity in the books tells me, no, they are not at the root of the rise in magic.
As far as other creatures/species, I haven't noticed information pointing to giants being magical, though they may have been the result of magic, like dragons. The wildings don't appear awed by giants so it doesn't seem as if they have become more numerous during this time of high magic.
I would guess the Children of the Forest are magical. The tales and myths of man that touch on the children are wrapped in magic. Also, they are said to sing the song of earth in the True Tongue, which sounds like magic. But I wouldn't say their magic is increasing, rather it appears to nearly be finished. Of the six children known to man, none have been reported to produce magic on a scale with what they are said to have done during the epoch-call great floods down to kill the first men. They harness magic, but the tone of the GRRM's writing makes it sound as if it is the same magic they have always possessed and their dwindling numbers is in lock-step with their magic dwindling.
The White Walkers or Wight Walkers (as some call them) appear to be a direct result of the rise in power/magic by the Night's King and the Others (I assert their mere return as a recent rise in the King's power, or why didn't he return sooner?)
I would say the Others sound the most tightly bound with magic, but I would not go so far as to suggest they are magical in nature. I like the idea of the red comet as the cause of magic in the world.