It's my reckoning that there are at least three different 'levels' of Doctor Who monsters. Obviously the top level is reserved for the Daleks and the Cybermen. On the next level, you'd find the Autons, the Silurians, the Yeti, the Ice Warriors, the Sontarans, the Mara, Sil and the Sea Devils. Then there are 'the rest'. Some of them are deservedly forgotten or have been seen only once probably for good reason, but…well, I adore them anyway. Here are some of my favorite unsung monsters listed in no particular order.

THE SENSORITES

They are the inhabitants of the Sense-Sphere who possess an incredible amount of mind powers including telepathy and the ability to control others minds over a long distance. They are deeply intelligent and civilized creatures who, having experienced exploitation by humans held a crew of humans, in a sort of semi-somnambulant captivity within their own spacecraft. These creatures have a genuine fear for their safety and the safety of their world. The Doctor, when he fully realized their situation, sympathized with them and helped them to resolve their crisis with the humans.

THE OGRONS

The Ogrons are exceedingly primitive, savage, physically intimidating brutes of limited intelligence that have served the Daleks on at least two occasions. Their home world is a barren, desolate place in which the Ogrons themselves are the prey of carnivorous giant worm-like creatures.

THE TRACTATORS

Tractators are huge, slug-like burrowing creatures who by nature are quite passive, but once they fell under the control of the Gravis, he used their collective magnetic powers to attract showers of meteorites to attack the human colony on Frontios for the Gravis' own nefarious plans.

THE DRACONIANS

Despite their fearsome dragon-like appearance, they are highly intelligent creatures that ruled a vast empire and fought on the side of the Alliance during the First and Second Dalek wars, however conflicts erupted between their empire and the Earth when areas of colonization came into dispute.

THE KRYNOID

The Krynoid are a carnivorous, parasitic weed, which travels through deep space in pairs and fell to Earth in approximately 20,000 BC and were buried in the permafrost of the Antarctic. When fully grown, the pods explode releasing thousands of their spores and on planets where the Krynoid gained control the vegetation would dominate and devour the animal life.

THE TERILEPTILS

The Terileptils are an intelligent, technologically advanced, war-like reptilian race. The few that the Doctor encountered were escaped criminals from the Tinclavic Mines of Ragga who found themselves stranded on Earth in 1666 and planned to destroy the human race by releasing a virulent strain of plague.

THE WIRRIN

The Wirrin are an insectoid life form, a parasitic breed that exists primarily in space, occasionally landing in search of food and for breeding purposes. Not unlike wasps on Earth, the Queen lays her eggs inside living hosts, however the Wirrin are capable of not only digesting the physical remains of the host but their intellect as well.

THE KROTONS

Blind crystalline beings that, although they look like robots, are creatures of pure tellurium who, after they were shot down during an interplanetary war, went into a form of suspended animation and survived on the intelligence of the Gonds. They are fully reanimated by combined intelligence of the Doctor and Zoe but once the Doctor realizes the Krotons plan to re-launch their ship, which will result in the destruction of the Gonds, he finds a way to defeat them.

THE CHEETAH PEOPLE

The Cheetah People are savage, cat-like humanoids with the ability to teleport through space in order to track their prey. They had a mysterious symbiotic relationship with their planet and as the violence of the Cheetah People increased, so did the planets volcanic activity.

THE KRAALS

An intelligent, evil, war-like alien race from the planet Osidon who, after nearly destroying their own world through a series of deadly atomic wars, planned to invade the Earth using their advanced android technology and a lethal virus.

There are plenty of others, of course, and everyone has their own favorites. Who can forget the Axos, the Borad, Drashigs, the Foamasi, the giant maggots, the Jocondans, Kronos, the Macra, the Malus, Mandrels, Mestor, the Ogri, the Rutans, Sutekh, the Urbankans, the Vervoids, or the Zarbi? This rich abundance of creatures has something for everyone.