(Note: this is a collection of the meanings attributed to the cards by some occultists in the past centuries. It does not reflect my own study or opinion of the cards. It is only meant as a quick comparative reference as I develop my own take.)

Paul Foster Case (and Ann Davies)

The time period is from the beginning of the last decanate of Sagittarius to the end of the second d ecanate of Capricorn, De cember 12 to January 9. This period combines the rulerships of the Sun, Saturn and Venus .
Well-Dignified: the ability to see the workings of Divine Law in the phenomena of the physical plane – thus rulership. In divination, a dark man, friendly to the Querent, practical, steady and reliable. He is good at the practical application of ideas and theories. Things tend to prosper and increase under his direction. He is slow to anger, but furious when aroused. Ill-Dignified: good theoretical insight into the workings of Divine Law, but inability to apply it to everyday experiences. In divination, a man selfish and materialistic. Such a man could have some power to solidify evil forces and express them but is nevertheless somewhat stupid.
(From the Oracle of Tarot course)

A. E. Waite

The figure calls for no special description. The face is rather dark, suggesting also courage, but somewhat lethargic in tendency. The bull’s head should be noted as a recurrent symbol on the throne. The sign of this suit is represented throughout as engraved or blazoned with the pentagram, typifying the correspondence of the four elements in human nature and that by which they may be governed. In many old Tarot packs this suit stood for current coin, money, deniers. I have not invented the substitution of pentacles and I have no special cause to sustain in respect of the alternative. But the consensus of divinatory meanings is on the side of some change, because the cards do not happen to deal especially with questions of money. 
Divinatory Meanings: Valour, realizing intelligence, business and normal intellectual aptitude, sometimes mathematical gifts and attainments of this kind; success in these paths. Reversed: Vice, weakness, ugliness, perversity, corruption, peril.
(From The Pictorial Key to the Tarot)

Aleister Crowley

(Note: Crowley and the Golden Dawn swapped around King and Knight. This is in part true of Waite as well.)
The Knight of Disks represents the fiery part of Earth, and refers in particular to the phenomena of mountains, earthquakes, and gravitation; but it also represents the activity of Earth regarded as the producer of Life. He rules from the 21st degree of Leo to the 20th degree of Virgo, and is thus concerned greatly with agriculture. This warrior is short and sturdy in type. He is clothed in great solidity of plate armour; but his helmet, which is crested with the head of a stag, is thrown back, for at the moment his function is entirely confined to the production of food. For this reason he is armed with a flail. The disk which he bears, moreover, is very solid; it represents nutrition. These characteristics are borne out by his horse; a shire horse, solidly planted on all four feet, as was not the case with the other Knights. He rides through the fertile land; even the distant hills are cultivated fields.

Those whom he symbolizes tend to be dull, heavy and preoccupied with material things. They are laborious and patient, but would have little intellectual grasp even of matters which concern them most closely. Their success in these is due to instinct, to imitation of Nature. They lack initiative; their fire is the smouldering fire of the process of growth.

If ill-dignified, these people are hopelessly stupid, slavish, quite incapable of foresight even in their own affairs, or of taking an intelligent interest in anything outside them. They are churlish, surly, and jealous (in a dull sort of way) of what they instinctively realize is the superior state of others; but they have not the courage or intelligence to better themselves. Yet they are always irritably meddling about petty matters; they interfere with, and inevitably spoil, whatever comes their way.

In the Yi King, the fiery part of Earth is represented by the 62nd hexagram, Hsiao Kwo. This is as important as its complement, Kung Fu (see under Prince of Cups); it is a “big Khan”, the trigram of Luna with each line doubled. But it is also suggestive of the Geomantic figure Conjunctio, Mercury in Virgo, corresponding very closely indeed with the Fire of Earth attribution in the Qabalistic system.

To the Chinese sages, moreover, the shape of the figure gave the idea of a bird. The meaning is, accordingly, modified by human influence of the more frivolous and irresponsible kind, Shakespeare’s “little wanton harlotry”, the French cynic’s “Souvent femme vane”, and the fickle mob of Coriolanus; indeed, of History itself. But Mercury in Virgo symbolizes Intelligence (and even creative Idea) applied to Agriculture; and this (once more!) harmonizes perfectly with the Ten of Disks, which is ruled by this Planet and this Sign. This adds to the superabundant mass of proof that this whole system of symbolism is based upon Realities of Nature, as understood by the materialist School of Science-if such a school survives in some obscure and obsolescent University! Such coherence, such introverted exfoliation, cannot be the chance parallelism of the dreams of nebulous philosophies.

The character described by this card is therefore exceeding complex yet admirably well-knit; but its dangers are indicated by the symbols of Luna and the bird. In the happiest cases, the qualities thus indicated will be romance and imagination; but overweening ambition, the pursuit of Ignis Fatuus, superstition, and the tendency to waste time in idle dreaming, are perils all too frequently found in such sons of the soil. Thomas Hardy has painted many admirable portraits of the type. Ill-starred indeed and black with bile are those who have profaned the Sacred Fire, not enkindling Earth to new, more copious, more varied life, but peering in deceptive moonlight, turning their faces from their mother Earth.
(From the Book of Thoth)

Golden Dawn’s Book T

A DARK Winged Warrior with winged and crowned helmet: mounted on a light brown horse. Equipment as the Knight of Wands.
The winged head of a stag or antelope as a crest. Beneath the horse’s feet is fertile land with ripened corn. In one hand he bears a sceptre surmounted by a hexagram: in the other a Pentacle like that of the Zelator Adeptus Minor.
Unless very well dignified he is heavy, dull, and material. Laborious, clever, and patient in material matters. If ill dignified, he is avaricious, grasping, dull, jealous; not very courageous, unless assisted by other symbols.
Rules from above 20 Degree of Leo to 20 Degree of Virgo.

Etteilla

Dark man.
Upright. This card, as far as the medicine of the spirit is concerned, means, in its natural position: Dark Man, Trader, Shopkeeper, Banker, Stockbroker, Calculator, Speculator. – Physics, Geometry, Mathematics, Science. – Teacher, Professor.
Reversed. Vice, Defect, Weakness, Defective, Defective conformation, Deformed nature. – Abnormality, Ugliness, Deformity. – Corruption. – Stench.

MQS