Genji Glove. Dual-wield weapons? Don't mind if I do!
The Offering. Attack 4 times at random? Holy crap, that's rad! And of course, their combination is legendary.
Speaking of amazing accessories in combination, the economizer as mentioned above, but also the jewel box that lets you double-cast. Putting them together was just rude.
Also in FF 6, for some reason the Hawkeye weapon always sticks in my head, and giving two of them to Locke. I think they were boomerangs or something? But they looked like some kind of thrown...mace bolo thing, and the arcing flight at the enemies was memorable.
FF8 wasn't my favorite but I have to admit I really like Squall's gunblades. THEY'RE COOL, OK, I'M SORRY