Here is a short overview over the planets, as far as it concerns Tarot. Sun and moon are listed as 'planets' as well, just because they are treated like that - so please: no emails please telling me that the moon is a satellite... ;)

The images below are my own design and no part of an unknown deck.

The sun is the symbol for life and light, the giver of life and the center of the universe (at least for the old astrologists who never watched Star Trek...).
The sun is taken as a male planet, attached to Leo and taken as responsible for a human's basic temperament and vitality (the 'inner light').
Most important gods of the sun were Sol (Rome), Helios and Apollo in Greek mythology, Mithras in Persia and Re, Osiris, Horus and Khepra in the old Egypt.
In Tarot the Sun is represented - of course - by the Sun.

_{The Sun is also connected to:
Three of Wands (Virtue) - Six of Cups (Pleasure) - Ten of Swords (Ruin) -
Four of Disks (Power) - Eight of Disks (Prudence)}

The moon always was attached to magic, fertility and the secret powers of nature. The moon reflects the light of sun and stars and therefore was taken as a funnel, collecting energy and pouring it out over the earth.
The moon is a female planet, a symbol for sensitivity and intuition, and its element is the water. In Chinese mythology the moon is standing for Yin and everything female, and nearly all moon gods are female:
Luna in Rome, Selene in old Greece, Astarte in Phonizia, Istar in Babylonia and Isis and Hathor in old Egypt.
In astrology, the moon rules Cancer. In Tarot the corresponding card is the Moon.

_{The Moon is also connected to:
Nine of Wands (Strength) - Four of Cups (Luxury) - Two of Swords (Peace) -
Seven of Sowrds (Futility) - Six of Disks (Success)}

(Mercur, Mercurius)
Ever since Mercury acknowledged as the planet standing for intelligence and reasonability, dexterity and education.
Like Mercur in Roman (Hermes in Greek) mythology Mercury is taken as a symbol for communication and reliability, while some prefer to forget that Hermes was the patron of the thieves, as well.
Not often mentioned is that Mercury was the chosen symbol of Hermes Trismegistos, the founder of 'hermetic' science, philosophy and literature, together with the Egyptian god of wisdom, Toth.
Therefore, Mercury was the planet of alchemy, as well and is usually attached to the Magician in Tarot.
In astrology, Mercury rules Gemini and Virgo.

_{Mercury is also connected to:
Eight of Wands (Swiftness) - Three of Cups (Abundance) - Six of Swords (Science) -
Five of Disks (Worry) - Ten of Disks (Wealth)}

Mars (Ares) is the god of war, therefore astrology takes it as a symbol for aggression, animosity, brutality and a strong will. The more positive aspects of Mars are courage, power and uncompromising steadiness. Mars is the ruler of Aries and Scorpio.
Little attention is paid to the fact that the day of Mars (March 15th), celebrated in all of old Rome, happened to be the same day (and the same feast) as the beginning of spring.
In Tarot, Mars is often connected to the Tower,but also to Passion (Strength), adding a sinister touch to the latter.

_{Mars is also connected to:
Two of Wands (Dominion) - Seven of Wands (Valour) - Five of Cups (Disappointment) -
Nine of Sowrds (Cruelty) - Three of Disks (Work)}

Beside Venus, Jupiter is one of the two benefit planets, standing for every possible positives. Being the father of all gods in old Greece (Zeus), he was told to be omniscient, wise and merciful, though he also was the god of thunder and lightning.
In astrology, Jupiter is standing for luck, optimism and abundance, and of course Jupiter is a male planet. He is the ruler of Sagittarius.
Jupiter is traditionally associated to the Emperor, yet in recent times people tend to connect him to the Wheel of Fortune. To me, for unknown reasons...

_{Jupiter is also connected to:
Six of Wands (Victory) - Nine of Cups (Happiness) - Four of Swords (Truce) -
Eight of Sowrds (Interference) - Two of Disks (Change)}

You'll rarely find someone seeing anything good in Saturn, as it's the planet known to have a restricting, hindering effect on nearly everything. Being one of the two Maleficum planets (the other one is Mars), it stands for everything negative, including influences and loneliness as opposed to high life and company.
Well, apart from the fact that the last point is a matter of opinion (as I DO prefer solitude in most of my life), it should be mentioned that Saturn was also the god of farming and harvest, and the master of time. In old magic Saturn is the symbol for science, independence and research, and in Tarot Saturn in Aquarius is the symbol for the Hermit.
In astrology Saturn is the master of Capricorn.

_{Saturn is also connected to:
Five of Wands (Strife) - Ten of Wands (Oppression) - Eight of Cups (Indolence) -
Three of Swords (Sorrow) - Seven of Disks (Failure)}