I can only think of a few that haven't already been mentioned in this thread. I poked around my inventory for a while tryig to remember them.
Acid/Teru Teru Bozu: The expression of the little charm changes depending on the position of your hand.
Panda/Pink Bunny Slippers: If you sit down and turn around they have a cute animal paw print on the bottom.
Winter Rose: If you equip the pose where your avatar is standing in the rose and sit down, you're just encased by the giant rose and the only thing popping out at the top is your avatar's head.
Inaris Beads: With one of the companion fox poses if you sit down, it sits down with you and rests its head in your lap.
Mini ufo: If you equip the pose of your avatar sitting in the ship then go to a flash space, you'll actually hover/fly around in the spaceship.
Those the only ones I could remember or stumble across in my inventory, I might think of more later.