Sasuke's Goddess makes an excellent point. Haku was the greatest weapon. It's hard to deny this as he himself said he was a tool.

I know it's stretching things a bit, but if naruto uses the Kyuubi that is still alive within him to fight, one could almost say that the Kyuubi itself is a weapon.

As a side note, this is my two hundredth post. Now to celebrate, I'll run around and possibly warp someone's mind just for amusement.