Sooo many...
I really like Luna because she is a Ravenclaw and doesn't give a damn about what other people think.
I also really like Bellatrix. Helena Bonham Carter plays her so well and I just love her character. It all just fits.
And I looove Severus Snape. His character development is amazing and his backstory, obviously. I think he actually might be my favorite. Oh wait...
McGonagall is really badass... I really love her... In general I love that Harry Potter has so many strong female characters.
And I have to admit that I always had a little crush on older Draco...