Oracles
While astrology may be the queen of all divinatory arts, the all time, undisputed king of the divinatory arts (and also the diciest) is the consultation of oracles. No system of card reading or wrinkle interpretation can exceed the authority of the oracle's direct link to the supernatural. Likewise, nothing else can be so easily faked, since its basis is mere assertion. Despite this liability to charlatanism, claims of oracular power have been met by eager believers for thousands of years. Some of the world's earliest civilizations were more or less run by the mandates of sibyls and illuminati. The Greeks, as usual, did it up best: the oracles at Delphi, Dordona, Didyma, and Claros flourished for hundreds of years. Notwithstanding what seems to have been a deliberate policy of sowing confusion, their proclamations were scrupulously obeyed.

The consultation process followed a rigid format, particularly at Delphi, which, like an exclusive restaurant, required reservations, since it was only open one day each month (the oracle took a three month vacation in winter, too). The oracle could be consulted by either individuals or states, though the cost for states was ten times higher than that for individuals, presumably because stately questions taxed the gods' patience more. Each month on the big day, three sibyls -- putative virgins who acted as mediums for the gods -- went into trances (induced by inhaling incense according to some sources) from sunrise to sunset. Once fully possessed by the divine spirits, the sibyl would emit then answer to the question at hand, but the attending priest, the maitre d' of the oracle, was the one who conveyed her statement to the waiting querent, often translating the answer into pithy verse. The priests exerted the real power at Delphi, since the sibyls could not be approached directly.
Delphi was the most ominous oracle, but Dordona was the most democratic. Less expensive than Delphi, it received more quotidian queries, which were written down on thin strips of lead and rolled up for secrecy. The priests of Dordona, who ritually did not wash their feet, interpreted the pronouncement of the oracle, which apparently lived inside an oak tree. Unfortunately, this interesting site has altogether disappeared.
Claros, the last of the great Greek oracles, had the most dramatic presentation. In the deep of night, querents were led single-file through a maze of passages underneath a great temple to Apollo. Finally, they reached a cavernous hall, where they remained while the sibyl continued on to the sacred fountain that inspired her trance.
The Greek oracles continued to prosper into the third century AD, though as the balance of power shifted Romeward, so did the balance of prophecy. The homegrown brand of fortunetelling in the Roman Empire was augury, divination by omens (example: if an eagle drops dead at your feet you're going to be an emperor), but oracles were also popular. Among the avalanche of papyri left by the documentarian Romans is a list of questions posed to a provincial oracle: "Should I remain where I am going?" "Am I to become a Senator?" "Have I been poisoned?"
The rise of Christianity put an end to the classical oracular tradition, or, rather, the Church transferred the authority to its own. The great desert fathers of Late Antiquity and the mystics of the Middle Ages filled the oracular shoes admirably. Hildegard of Bingen, a 12th century nun, is a case in point. Immured from the age of eleven in a small nunnery on the Rhine, she became famous for her visions and ensuing edicts. According to the pictures she bid her faithful scribe to draw, the spirit came down on her head in tongues of flame and she wrote the words it told her. She was consulted by peasants and lords for miles around -- she was, in some ways, a pilgrimage destination -- and she freely dispensed opinions and advice that were, she said, not hers but God's. Nervous at this special access to the divine, Saint Bernard of Clairvaux told her to stop it, and she did.
The Enlightenment put a damper on the oracles of Europe, but the Romantic Era fanned the flames. Séances held by mediums became fashionable in mid-nineteenth century Europe, and England, particularly, was gripped by a frenzy of trances, spirit visits, and table tilting. This latter -- a predecessor of the modern Ouija board -- was the parlor game of choice in the Victorian Era. A somber group would gather round a small table in a darkened room. Each person laid a single finger on a tabletop while one posed a question. After a few moments, the table would heave up one leg and crash back down again. That number of "tilts" revealed the answer -- one for yes, two for maybe, three for no. Stuffy Queen Victoria herself once played at table tilting.
Like the tilting table, the Ouija board's workings are inexplicable, but work it does. To consult Ouija, you and a partner lay your fingers on a small, heart shaped stool that rests on a board containing the words "Yes," "No," the alphabet, and numbers. After you have asked a question, the pointed end of the stool will move from spot to spot, spelling out your answer, which can be quite alarming in its prescience.
Almost every oracle has been accused of fraud (or bad faith), but they persist. Perhaps this is a testament to humankind's gullibility, or perhaps it is a sign of the eagerness of the inhabitants of the other world to help us.