Mojo will turn you into a frog if you /kiss him.
Penguins will do a belly slide if you /sexy at them. At least named once do.
Titooccasionally summons tornado that has some neat animations.
Fox kit dances.
durotar scorpion will random 'sting' you
mr grubbs randomly backflips over you
Feline Familiar will mount on a broom and fly after you (unlike most ground animals)
Lashtail Hatchling will dig up bones from things you kill and carry them around.
Nuts dazes you with nuts.
perky pug scoots its butt on the floor (bad dog!)
stinker will chase black tabby (pepe le pew reference)
spring rabbits will hump each other and leave little eggs everywhere
Egbert darts off.
Mulgore Hatchling goes crazy in Ironforge AH
Ony whelp emotes (name of pet, takes a deep breathe).
Blossoming Ancient will grow flowers around him (changes colors by season).
withers will grow if theres a puddle nearby and he stands in it
kirin tor familiar randomly arcane explosions
Frigid frostling throws snowballs all the time at nearby players.
Lil Ragnaros burns lvl 1 critters around "By fire be purged".
Singing Sunflower chases undead near Cathedral and casts something that resembles a healing spells on user.
Searing Scorchling with randomly float over to lvl 1 critters and set them Ablaze
Teldrassil Sproutling used to take naps and dance sometimes
Tiny snowman will /dance with you during the winter veil season.
Moonkin Hatchling also plants flowers occasionally.
Tuskarr Kite gets bolted and bolts you with lightning.
plump turkey will jump into nearby basic campfires and cook itself
Fiendish Imp when summoned comes out of the nether portal.
Pandaren Monk will /bow and /drink with you.
Moonkin hatchling with /dance with you.
Disgusting Oozling will give you the debuff, Oozling's Disgusting Aura, which turns you green.
Disgusting Oozeling will also drink beer if you throw it. http://www.wowhead.com/item=11325
Toxic Wasteling eats critters and grow bigger each time it feeds.
Willy will occasionally zap critters with his Eyebeam.
Ethereal Soul Trader harvests soul essence and acts as a vendor.
Lil XT kills not just trains but many other mechanical pets/toys.
Rocket chicken lifts off, and occasionally will blow up.(I love him *squeezes)
Battle Bots occasionally attack each other if near.
Unborn Valkyr will resurrect nearby dead critters every 30 or so seconds.
Lil KT freezes critters in an ice block.
Lil KT in Nax he'll frost bolt Mr. bigglesworth, sit on the throne (after you kill KT).
Crawling Claws will play rock, paper, scissors with each other.
Creepy crate will randomly death grip critters to eat