I like the idea of someone as a Seer, but I think it's Ron.

I think it's Luna. She acts just like Trelawney does, only it's for real. My theory is that Trelawney heard stories about her great-great-grandmother acting that way and decided that's the way true Seers act, so she started acting that way, too. Luna is also very eccentric and seems to know things other characters don't, so I think she's the real thing.

Or it could just be that it fits in with my time-traveling!Sirius theory for Luna to be a Seer and that's why I'm hoping it's true. Heh.