I saw your post in the 1001 magic items thread; here are some I whipped up for the various supernatural animals that classes can obtain (I restricted them to such creatures to justify the cost reductions).

Cap of the Familiar
This tiny conical cap is made from fine dark blue velvet and sewn with silvery stars and crescent moons. It may only be worn by the familiar of a sorcerer or wizard and grants the familiar the ability to use light, mage hand, and prestidigitation at will.
Faint universal; CL 1st; Craft Wondrous Item, light, mage hand, prestigidigation. Price 900 gp.

Collar of Ferocity
This rough-hewn adamantine collar may only be worn by the animal companion of a druid or ranger. It grants its wearer a +6 enhancement bonus to their Constitution, Dexterity, Strength, and Wisdom scores.
Moderate transmutation; CL 10th; Craft Wondrous Item, bear's endurance, bullís strength, cat's grace, owl's wisdom; Price 33,000 gp.

Horseshoes of the Celestial Steed
These four mythril shoes are affixed like normal horseshoes but may only be worn by a paladin's special mount. They grant the mount the celestial creature template and a fly speed of 40 feet with average maneuverability. All four shoes must be worn by the same mount for the magic to be effective.
Moderate transmutation; CL 10th; Craft Wondrous Item, holy sword. Price 20,000 gp; Weight 4 lb. (for four).