Some interesting Beasts not yet claimed, for those of you who are still searching... :)

Shadhahvar: In Persia a single horn was the symbol for the highest cruelty and danger and therefore the Shadhahvar was regarded as a dangerous beast. It was described as a creature that looked somewhat like an antelope yet with a single horn on its forehead. This horn had hollow ends which created the most beautiful and tempting melodies when the wind was blowing through them. Other animals who heard these melodies were lured out of their hiding places by the sound and killed by the Shadhahvar at the very moment they had come too near to it.
Theow (aka Thea/Thos): A wolf with cloven hooves instead of paws and a mane of many colors.
Mermecolion: Creature with the head of a lion on the body of an ant.
Gansas: A swan with one webbed foot and one taloned one. Every year they migrate to the moon.
Martlet: A bird with no feet. It catches its food while flying, and therefore it appears never to stand on the ground.
Tetramorph: Described by Ezekiel as having the face of a man on the front of their head, the face of a lion on the right side, the face of an ox on the left and the face of an eagle on the back, six pairs of feathered wings (one par held upward, one spread to the either side, and one pair folded in front to cover the body), with "eyes" (or peacock-like eye-spots?) all over the top and bottom of their wings, with the torso, arms, hands and legs of a man, and the feet (hooves) of a calf. See this and this for more info.
Goose Tree/Barnacle Goose: A type of goose that grows on trees, and then drops into the water. Some people thought that these geese hatched from barnacles, and were thus able to eat them on Friday, since they were considered to be fish, not meat.
Sirrush (aka Sta): This creature is serpent-like, with the scaly head and skin of a snake, the forefeet and tail of a lion, and an eagle's talons for hind feet.
Ypotrill: Has a camel's humps, a boar's face, and cloven hooves. (Some depictions show it with a snaky tail.)
Vegetable Lamb: A stalk-like plant whose blossoms "issue a lamb". According to legend, once the lamb-blossoms have eaten all the vegetation within their reach, they die of starvation. Also according to legend, the vegetable lamb is considered a delicacy as its meat tastes like fish, and its blood like honey. Its bones can be used in rituals to give human beings the power of prophecy. Also called: Barbary Lamb, Barmotez or Tartary.
Bonacon: Also known as a Bonasus. A bull-like (or bison-like) creature with horns which curl inwards, a horse's tail and a short mane. Its horns were considered useless, but the creature was reported to be very dangerous as it defends itself by shooting burning excrements at its enemies. XD

P.S. This tidbit about the Bonacon cracks me up: "First noted in heraldry as a crest granted to Richard Chandelor in 1560. At present the SCA College of Arms has a precedent again the registration of such a monster: 'The bonacon was considered too offensive by a significant fraction of the College and is therefore not allowed for use in the SCA.'" Sissies! XD

~SD

Edit: The Shadhahvar, the Tetramorph, Barnacle Goose, Sirrush and the Theow have now been claimed. :)