There are a number of ways that religious thinkers have traditionally approached this topic; many widely differing views have been proposed. Generally speaking, one can find all of the following viewpoints in varying segements of Judaism and in varying groups within Christianity.
Verbal revelation
Some people hold that God can communicate with man in a way that gives direct, propositional content: This is termed verbal revelation. Orthodox Judaism and traditional Christianity hold that the first five books of Moses were dictated by God in such a fashion.
Aristotelian rationalism
The neo-Aristotelian philosophers of the medieval era held that revelation was the discover of absolute truths about God, man, and man's place in God's universe, as discovered through logical philosophical inquiry. A prophet's connection to God was held to be the only way that a person could reach such a state of pure reason.
Non-Verbal propositional revelation
One school of thought holds that revelation is non-verbal and non-literal, yet it may have propositional content. People were divinely inspired by God with a message, but not in a verbal-like fashion.
Rabbi Abraham Joshua Heschel has written that "To convey what the prophets experienced, the Bible could either use terms of descriptions or terms of indication. Any description of the act of revelation in empirical categories would have produced a caricature. That is why all the Bible does is to state that revelation happened; How it happened is something they could only convey in words that are evocative and suggestive." ["God in Search of Man"]
God's will as revealed through a people's historical development of their faith
Some believe that given God's non-anthropomorphic nature, the above listed forms of revelation are, by definition, impossible. Thus, God's will is revealed through the interaction of man and God throughout history.
For instance, Rabbi Louis Jacobs proposes that by viewing how the Jewish people have understood God's will throughout history, we see how God has actually influenced the development of Jewish law; it is this process that we should recognize as revelation.
[Similar texts from other religions would be good to add here!]
Existentialism
In the 20th century, religious existentialists proposed that revelation held no content in of itself; rather, they hold that God inspired people with His presence by coming into contact with them. The Bible is a human response that records how we responded to God.
For information on the last book of the bible, see Book of Revelation
Revelation or information from a supernatural source is of much lesser importance in some other religious traditions. It is not of great importance in the Asian religions Buddhism, Taoism, and Confucianism.