I know that Edward refers to himself by the assertive "ore" and that Alphonse uses "boku"
I'm pretty sure I heard Winry use the feminine "atashi" and I heard Mustang say "ore"
I can only assume that Envy uses the gender-neutral "watashi" if he's supposed to be as ambiguous as he is, but I haven't paid too close of attention to his speech patterns, partly because he changes so much. Greed, I'm pretty sure, uses "ore."
What about the others? How do the various characters refer to themselves? Do most use the generic "watashi" or do a lot of the guys use "ore"?