CLAMP is a widely-respected all-female team of manga creators, whose artistic style is iconically androgynous and whose themes also work to blur gender lines.
Over at Quickand2thePointless: Adventures in Animeland, a fellow Blogger has already addressed their work in a post that's rich, insightful, and anything but pointless: The review Lost in Translation: Androgyny in Clamp's RG Veda and Wish discusses the powerful messages implicit in CLAMP's use of gender ambiguity, and how the inability to maintain genderless address in English translation may hinder those messages.
Drawing on author Julie's line of thought, I'd like to particularly acknowledge the character of Kohaku, from the four-volume CLAMP manga Wish (1997).
