Recommendations for Stories Exploring Gender

I'm looking for stories, fantasy, sci-fi or speculative fiction in general, where there either is no gender at all or where the genders, or gender roles, are different to those of our own world, or perhaps change or are in some way in dispute. I feel like there is huge potential in fantasy for explorations of post-gender or differently gendered societies, but I haven't really come across any such stories. Any suggestions?