We currently have a player who possesses a "bag of apples," but rather than containing an endless supply of apples it instead converts/disguises any roughly apple-shaped/sized object into an apple. She can pull out specific apples, without mixing them up, as though it were a handy haversack. The apples retain their chemical and magical properties.

Bracers that look like animal heads, that enlarge and engulf the wearer's fists when activated, giving them a bite attack at the end of each arm. The bracers came in a wide variety of types/species, with slight variations on the bite damage and effects. The bite attacks were considered natural weapons.
Wolf: 1d6 bite + trip
Snake: 1d4 bite + poison
Dragon: 1d6 bite, can cast burning hands 1/day at CL 5th.
Rat: 1d4 bite + 1d6 sneak attack (if applicable)
There was even a two-handed dragon variant, where one hand would be made into the lower jaw, and the other into the upper jaw. It only worked when used in unison, but dealt 2d6 damage + 2x Strength

One of my players was granted a wish, and asked for his adamantine greatsword to become "the most feared weapon in history". I gave it a bonus to Intimidate checks, and 3 charges of disintegrate. He could cast a charge as a swift action after hitting with the sword, and the caster level was equal to his base attack bonus.
He, of course, hoarded the charges and never used them, but what he didn't know was that there was a 33% chance that any charge he tried to use would affect him, instead of the subject of his attack. The idea being that the sword, after striking down its wielder in such a fashion, would become the most feared item in the world, so much so that no hero would dare to use it, for fear of their own life.

Gave a character a dagger that started off really weak, but dealt increasing damage with each worthy adversary that was killed with it. The campaign ended not too long after he figured out what the power was, so he never got it unreasonably farmed, but for a while he was really stab-happy.

Gave a character a bag which contained roughly 50 items, though he was allowed to draw out only 1 item at a time and he had to wait 1 minute between draws. He also could not keep an item out of the bag for more than 1 minute. His draws were, of course, random. It ended up being a terrible idea, though we had a lot of fun with it.
The bag included, among other things:
A portable hole/pocket dimension in a top-hat, into which he could throw enemies to remove them from a fight for 1 minute.
A piece of the grim reaper's scythe, able to kill any creature with a successful attack.
A pair of strap-on wings that allowed him to fly very quickly.
A poke-ball (it was a strange campaign, set in modern times, and they encountered a genie who could make one imaginary item become real)
Batman's utility belt (see above)
and a bunch of other, mostly useless items.