I found a couple weapons that were not included in the official guide, and they have comparable strength, if not more, than their ultimate weapon.

Aeris can equip the umbrella that you get in the Speed Arena in GS, and it has better attack than Princess Guard.

I found the Behemoth Horn for RedXIII in the Shinra stairs on my own. A random gamefaq says it's a couple points less than Limited Moon, though.

Where else can I find these kinds of weapons? Are there any other weapons that the official guide missed or is stronger than one's ultimate weapon?