Major book recommendation: Ancillary Justice by Ann Leckie. It's a Nebula nominee *and* on the Tiptree Honors List, and I would not be at all surprised to find it a Hugo nominee as well. It is good enough that I have just finished it and am already going back to re-read the first chapter.
To begin with, it is a really good story with strong writing. But beyond that, it will make you think about identity/personality and gender in a way that you might not have before. Also, while it is the first book in a "loose trilogy" and I look forward to reading more, it didn't leave me with that sinking feeling I usually get when I discover that a new book I am reading is the first in a trilogy, meaning I have to wait years before finding out the whole story. The book end with many threads to continue the story, but with enough closure to make you feel like you really finished reading a novel.