Quina's fork is epic, but i think the reward goes to Eiko and her flute xD

Cait Sith's megaphone and trumpet was interesting and all the special weapons in FFVII.
Vincent's hairblower, Barret's boxing glove, Red's hairpin etc.

And out of FF, Demyx sitar was weird and in Shadow Hearts, Alice book/ancient tomes she actually attacks with them, it's really funny.
And Joachim uses objects only for weapons, like ancient ship of dead people, tuna fish and so on.