Reins of Equine Sundering

These modestly decorated leather straps have no effect unless they are used as the reins of a horse. A horse and rider equipped with the reins of equine sundering can, running at full speed, charge through barriers – up to 6 inches thick of wood, or 3 inches thick of stone or metal – without being harmed.

Getting the horse to run at full speed into a wall like that is entirely up to the rider.

If the horse hits a barrier twice as thick as that, the horse will instead explode, inflicting 4d6 damage to the rider and anyone else in a 15-foot radius. Less than that (but more than 6 or 3 inches) and the horse will merely suffer 1d8 points of damage.

Palette Tattoo - The exact design of this magic tattoo varies, but it always includes at least seven distinct colors, more if possible. At will the tattoo's bearer can cause any individual patch of color to secrete the appropriate paint, just enough to coat a paintbrush with.

Omni-Cameo - This pretty locket contains a nicely sculpted cameo of someone's profile. While the locket is closed the wearer can will it to change the cameo into a flattering image of anyone the wearer has seen. The image stays that way until someone changes it again.

Popular with seducers who need to impress multiple conquests at a time.

Maybe a bit to useful for this threat, but it is the best place I found for it:

Sleeping Hat of the fuzzy and cute: When worn during sleep, this pink fuzzy hat with adorable kitten ears ensures that the user has nice dreams filled with kittens, puppys, smiling suns and other mind-numbing cute things. In addition the user looks so adorable and peaceful as to be considered under the affect of a sanctuary spell during sleep.

However, any sleep under the effect of this item is extended to last 12 hours and only pain (at least one point of damage) can wake the user. If awoken before 12 hours of sleep have been taken, no effect of rest is gained.

Sarcophagus of Pet Renewal - This little gold sarcophagus is just large enough for an average-sized dog and is decorated with kitschy scenes of disturbingly wide-mouthed children playing with various animals. If a deceased animal* with no special properties is left inside the sarcophagus overnight it returns to healthy life and in pristine youthful condition.

The creature counts as undead but otherwise acts as it always did. It no longer eats or drinks however; instead it unknowingly drains the life-force from any nearby humanoid children. Once a "playmate" has been sucked dry (a process that takes at least six months and produces symptoms that resemble a very forgiving wasting sickness right up until the end) the bereaved animal feels compelled to seek out new children to befriend before it too starts to wither.

*No humanoids

The Dire Hedgehog - a small felt, fuzzy bag, any object placed inside of which turns to a mixture of peanuts, caramel and chocolate.

Horn of Snow Clouds - This chunky horn is sky blue and carved with alpine scenes. Blowing into it once per week produces a cloud 200 feet in diameter that quickly drifts up into the air until it is floating about 15 feet off the ground. The cloud then produces gentle snow that gradually covers everything beneath it over the course of a half-hour. Afterward the cloud dissipates.

The snow is the ideal thickness and consistency for sledding, and magically withstands normal weather conditions for at least three hours (more when it's cold).

Grayscale Sponge - When dry, this round black sponge can be used to instantly wipe the color off of anything, leaving nothing but shades of white, grey and black. This "decolorization" lasts until the magic is dispelled (which is very easy to do for even apprentice mages) or the sponge is submerged in water.

Popular at high-society events where novelty is prized.

The Cast Iron Monkey - a small frying pan carved to resemble an ornate monkey head. The pan makes everything it cooks taste like bananas.

Plant Magnet - This horseshoe-shaped yellow lump of metal functions as a powerful magnet, but affects plant-matter instead.

Tenacious Trick Belt - This impressive black leather belt has a dark bronze buckle shaped like a grinning ogre face with a spectacular handlebar mustache.

Once you put on the belt, it becomes bound to you until you die, gift it to someone else, leave it off for a week, or somehow lose your waist.

If you are not wearing it, you can utter the command phrase "Belt, show everyone what you can do" and the belt will crawl toward you like a caterpillar, wind its way up your leg, and fasten itself around your waist.

The belt can be summoned from anywhere in the world, as it doesn't actually need to hear you. It will stop at nothing to reach your waist, and has the strength and toughness of an ogre. Those who get in its way will be firmly tossed aside, and objects that block its path will be battered down. Anything tied to it will be dragged along. It can spring ten feet into the air to clear obstacles and can swim like a snake.

Note that the belt cannot be commanded to stop, even by you, and only the most powerful abjuration magic can interfere with its powers.

Medal of All Conflicts - This plain-looking military medal has a subtle charm on it. People interacting with the wearer unconsciously assume he or she has served with distinction in some recent war that the charmees are aware of and react accordingly. This can help the wearer lie about the conflict, but too many blatant problems in the story can dispel the effect. Note that the wearer doesn't automatically know what war the charmee will think of.

The Perfume of Abdullah Al-Qahar:  a small vial of perfume, even a drop of which can remove the scent of even the worst grime.

Ring of Last Words - This black ring has an ornament that combines an image of a mouth with an open casket.

If the wearer is mortally wounded, he is guaranteed the opportunity to gasp out a maximum of a minute worth of lucid speech before expiring. This cannot be used to cast spells, and the wearer is in dramatic pain the whole time. The wearer's voice is also subtly amplified so it can be heard at a greater range without causing discomfort.

If the wearer is healed at any point during his/her last words, the ring breaks and he/she is cursed with eternal muteness.

From an old 2E AD&D campaign treasure trove.

large jar with head in amber liquid (seems to be aware): head is one Ewar
Farrar (LN), an apprentice Necromancer who cheesed off his mentor, he has
been in the jar for 78 years (43 of them in his masters den). Outside of
the jar he will quickly die.

conch shell: has four hours of music recorded on it, popular symphonies.

medallion w/ 17 moonstones: a magic compass, always knows North and can
'tag' an object for tracking.

blade (24" long, 3" wide, 1/4" thick, straight with D-style guard and
beautiful wood grips): blade will cut wood and plants without effort,
leaves the plant unharmed, will not cut any other substance.

27 sheets of vellum in leather scroll tube: pages can accept 'images' from
a mage using them, will record anything the mage is looking at when command
word is used ( Flash!).
 
lidded medallion on chain: 'pocket' clock, tells time (hour, minute,
seconds), date, has chime (hourly, every ten minutes or every minute) and
has hologram of dancing girl (seven veils strip).

gold nightengale (life sized): automaton, functions like real bird, has
switch and will come when called.

pheonix feather quill: has endless supply of mundane ink.

ivory cube (1" x 1" x 1"): 'icecube', will cool up to a gallon of liquid
down to any temp. short of freezing in one minute, can be used for one hour
per day.

8" pot w/ attached lid: lid attached by short chain, will self heat (up to
1000 degrees), must rest for equal time period used, maximum of twenty four
hours use at one time.

flask of blood: vampire blood, one pint.

glass sphere (15" diameter) with small blue demon inside (appears  unhappy
and aware of it's surroundings): entrapped minor demon, sphere has had
Glassteel cast on it, opening the sphere will release the demon, demons
name is Takoupla and is LE.

invisible ring: gold ring which is invisible.

gold handled folding straight razor: magicked to never dull or rust.

dram container of clear liquid: medusa's tears.

broom: automatic broom, will clean one square yard per minute, will work
for up to 12 hours per day.  

3' steel bar w/ seam at center and textured grips to either side of seam:
a "static" bar, when the two sections are twisted in opposite directions
from each other the bar will "lock" itself in place until released, bar can
be "locked" in midair if desired.

An invisible medium round shield: shield is simply invisible, opponent
gets a -2 on attacks first round due to surprise.

black leather war kack: Saddle of Security.

black cloth (1' square): Cloth of Polishing.

mahogany box (3' x 2' x 2', with hinged lid): Box of Preservation.

gray wool blanket (6' square): Blanket of Comfort, keeps the user (can
cover two M sized persons) at their preferred temp. (can adjust up to a
60 degree temp. difference).

teak handle set with tattoo needles: Needles of Tattooing, needles have
endless supply of tattoo ink in up to 256 colours, needles are also sterile
at all times.

silver coin: a coin with a Magic Mouth cast upon it (set to release when in
the presence of a green elephant carrying nine red pygmies).