Haku: My favorite ninja, and arguably the potentially most powerful ninja in existence.
This child prodigy with a Kekei Genkai that combined Wind and Water jutsu to naturally, almost magically wield Ice Style brought so much death as Zabuza's loyal tool. It's almost insane to imagine how it took the power of Kurama in naruto to match his speed.
Besides his beauty and personality, Haku is one of the best characters, both in design and story, it still *s me away such an amazing character was taken out so early in the series.
Tayuya: Flute playing was beautiful, genjutsu was so useful and nicely done, and beyond all that, her personality... well, it's been said in this thread already, but beyond that, yes, just amazing.
Kabuto: A strange choice, but yes, Kabuto is one of the most devious characters in the series, He is also my favorite, his conniving nature, abilities, and the decisions he makes prove he is so much more evil than most of the villains in the show. His absolute devotion to ruining others, growing stronger and all that deception.
His character baffles me in so many ways, that the only way to explain a lot of his actions are pure evil. Experimentation, psychological damage, and betrayals abound. But beyodn that, I like his design before he becomes... a ... Sage dragon. He both resembles an assassin and a medic, which sums his character up quite well in some ways.