|Maybe they don't suit your tastes, so I apology, but extraordinary stories for me are:
Gunslinger Girl. I love everything about it. Can fit for 1 I think, the girls are getting weaker, some of them becomes even "useless".
Hakomari. It's a novel though, but it's amazing. Can kind of fit for 2, since some friends become enemies later on. Also what I found unique and fresh is that BIG SPOILER AHEAD don't read it if you ever consider to read the novel:
Spoiler (mouse over to view)
in volume 5 it's revealed that the main girl chose another character as first partner to work with in order to stop the anomaly of the time reset in volume 1, which I found quite peculiar. Obviously only her knew it, since only her retained the memories after the time reset, but in this kind of story usually the bond between main girl and main guy is never questioned like this.
What I like in Trivial Pursuit style. Pick your category: