Catherynne M. Valente is one of my favourite authors. I first discovered her through her short stories, many of which can be read online at the websites of the magazines that published them, but I really fell in love after I started reading her Fairyland books. She has also written numerous speculative fiction novels including Radiance, Palimpsest, and The Grass-Cutting Sword, and she has won many awards for her work. She was actually at Finncon last year, and I'm really bummed I missed it.
There's something very intriguing about the way the Fairyland books mix myth and magic and pure imagination, and I loved the little winks at all the children's books I love, like Alice in Wonderland, Peter Pan, and Narnia. The main character, September, is wonderfully gutsy; she's no fairy-tale princess waiting for a prince to rescue her. Valente's style is quite distinctive and original, and even in her young adult books she doesn't shy away from the big words. She also writes poetry, which shows in her prose as well. (In a good way, I think.) For writers there's an added bonus: if you want to learn about crafting unique metaphors and similes and beautiful prose, Valente's a great teacher.
Here's an excerpt from Valente's first Fairyland book, The Girl Who Circumnavigated Fairyland in a Ship of Her Own Making:
"All children are heartless. They have not grown a heart yet, which is why they can climb trees and say shocking things and leap so very high that grown-up hearts flutter in terror. Hearts weigh quite a lot. That is why it takes so long to grow one. But, as in their reading and arithmetic and drawing, different children proceed at different speeds. (It is well known that reading quickens the growth of a heart like nothing else.)"
You can read more about Valente on her website and there's also a list of her short stories with links to the magazines if you want to check her out.