Ideas for devil fruit:
Ant Ant fruit: model Queen
Turns you into an ant queen. In full ant queen mode you can give birth to drones, each of which is like the original user but with relative ant strength and ant powers. The downside is that in queen mode you're too fat to move, and the drones you create have ant intelligence, and only communicate by pheremones.
My idea is basically that a guy (lol) eats the fruit, created an ant colony around himself, and now he's stuck in there and terrified to leave, because the second he changes out of ant mode he'll get killed by the absurdly overpowered ant drones, and while he's in queen mode he's too fat to move.
Other fruit:
Candy candy fruit
A paramecia that gives you the power to create candy. It's limited to pure sugar-based candies, though ("the power of sugar"). No chocolate or anything fancy like that. Just marshmellows, candy canes, etc. He usually fights with a candy cane sword, uses pixie dust to blind the opponent, etc. Ultimate power is turning into the giant marshmellow man from the ghostbusters.
Acid Acid fruit:
There are a bunch of limitations on this fruit to keep it from being too similar to Magellan's. First and foremost, the character doesn't generate acid, his body and its fluids are simply already acidic. The guy I have in mind is an assassin-type, and the most basic application of his power is simply using martial arts where your attacks eat right through the opponent (and if the opponent hits you without accounting for your weakness, their hand gets eaten away).
Additionally, he has a bunch of abilities relating to vomiting. This is the only way for him to use projectile attacks, and it works basically like a hose, he can't control it like Magellan. Ex, he can't create a dragon or anything, but he can shoot a solid concentrated stream ("Hydro Pump", as in hydochloric acid...), a diffuse spray ("Acid Wash"), or shoot it into the air and have it fall back down as droplets ("Acid Rain"). He keeps a sword and various weapons in his stomach (which he can make non-acidic), and pulls them out Orochimaru-style.
If someone figures out his weakness (bases, like soap and baking soda), he can acid etch a sword (removing rust, imperfections, etc, and making it perfectly sharp) by swallowing it and use that to fight.