I'm assuming we're not counting Avatar: The Last Airbender. Anyway, my most attractive female animê character is Lust from Fullmetal Alchemist. My seguinte choice would be Lady Amalthea from The Last Unicorn. As for my most attractive male animê character, it's a hard choice because I'm not a fã of the style, but I guess it's Prince Charles from cinderela Monogatari.
Amalthea isn't from an animê though. Her movie was made in the USA. Her movie may have a slight anime-inspired design but it's NOT anime.
With that said...Halle Lidner from Death Note, Kiba and Blue from Wolf's Rain, and Yoruichi and Urahara from Bleach are some of the most attractive animê characters I've seen (Yoruichi reminds me a lot of a young Eartha Kitt for some reason). In Digimon most of the humanoid Digimon are kinda attractive- Angemon, Sakuyamon, Beelzebumon, Wolfmon and Agnimon are some of my favoritos in terms of "attractive designs".
If we count Studio Ghibli movies, then I find Howl very attractive as well.