I can't think of any other truly androgynous characters (where you really don't know what their gender is ever if there is any), but there's always been a good deal of mystery as to Yuri Kamanosuke's true gender in Brave 10. I couldn't be certain of the gender from just watching the show (had to look it up).
For me Count D from Petshop of Horrors is an androgynous. He was always mistaken as a girl/woman throughout the manga series. His fashion also is quite feminine, he even wears make up and nail polish. How I wish they'll continue the anime series 'coz I want to see a lot of him in anime.