If I could get someone to make the costume for me...
Tali, from Mass Effect
Kaine, from Nier. Although I might need to be drunk first.
Yuna, from FFX. I'd need to cut my hair for that one, though...
I've already done Aeris (FF7), Shiori (Utena), and Yukari (Persona 3), but those were mostly easy. Also, I didn't make any of those costumes either. I am terrible at costume design (other than accessories, at which I am a master).
At one point there was talk of a Sailor V costume, but it never happened.