So, for serious (or usable) responses so far, we have:
Goblins -- Insult humans in broken Common, make rude gestures, throw filth on them, etc. -- but only from out of reach. Break fences, steal livestock, etc. to extort cookies from human farmers.
Hobgoblins -- Goose step. Always march in order with magnificent battle standards and symbols of power. Shout a battle cry in unison before charging.
Gnolls -- Cackle eerily. Females dress like males, may be chieftains. Hate lions, even heraldric designs thereof.
Ogres -- Slam their clubs into the ground before battle (to challenge and scare the opponent). When charging, throw around stuff laying about (overturning tables, throwing pots and pans, etc.).
Minotaurs -- Throw their heads back, roaring in defiance. Before charging, scrape their hooves along the floor (like bulls). Chase their prey at leisure, their loud footsteps echoing through their mazelike lair -- since they dont have to rush; they already know where to turn.
Hill Giants -- Lick boulders before throwing them. Love to throw with their mates in waves. Wear multicoloured kilts. Clap their hands after hitting and holding up their fingers to give a rating of their throw.
Kobolds -- Never stand still (except when they're lying in ambush, of course). Even in melee combat, they're continually taking 5' steps at the very minimum.
Displacer Beasts -- Usually napping. Watch birds, squirrels, and other game. Try to scare off enemies after making a kill (to eat safely).
Giant Owls -- Eat Were-Rats and Ratmen. Regurgitate giant pellets (maybe with treasure). Always looking around -- turning their heads 180 degrees.
Treants -- (In tradition of Tolkien's Ents...) Live in geologic time. Speak slowly and laboriously, never succinctly. Remember ancient history.
Blink Dogs - Wag their tails before 'blinking'; like to stand on their hind legs; love to drive normal dogs crazy by blinking in and out.
Hags -- Offer tasty treats. Very maternal and sweet -- until upset. Hate beauty.
Celestials -- Speak in riddles. Only make formal declarations, no small talk. Look through people.