Babylon, mentioned six times by name in the book of Revelation (Rev. 14:8; 16:19; 17:5; 18:2, 10, 21), plays a significant role in the events prior to the Second Coming of Jesus Christ. As with almost all other aspects of the book of Revelation, in order to understand what Babylon is and what it is not, it is important to recognize that the book of Revelation is the capstone of many streams of prophecy which find their source elsewhere in Scripture, and especially in the OT. In a similar way that Genesis and Revelation serve as bookends around God's written revelation, Babylon also has great significance both in the beginning and end of God's plan in history.
The earliest mention of Babylon and the region it occupies, the land of Shinar, is found not long after the global flood:
Cush begot Nimrod; he began to be a mighty one on the earth. He was a mighty hunter before the LORD; therefore it is said, "Like Nimrod the mighty hunter before the LORD." And the beginning of his kingdom was Babel, Erech, Accad, and Calneh, in the land of Shinar. From that land he went to Assyria and built Nineveh, Rehoboth Ir, Caleh and Resen between Nineveh and Calah (that is the principal city). (Gen. 10:8-12 cf. 1 Chr. 1:10)  (emphasis added)
It was Nimrod who established a kingdom at Babel. In fact, this is the first mention of the concept of kingdom in Scripture. In a very real sense, Nimrod was the first king. And in order to be a king, one needs to have subjects and a realm. This implies centralization in a way which ran counter to God's command following the flood: "Be fruitful and multiply, and fill the earth" (Gen. 9:1, 7 cf. Gen. 1:22, 28). Reading between the lines, we can already see the seeds of rebellion.
Now the whole earth had one language and one speech. And it came to pass, as they journeyed from the east, that they found a plain in the land of Shinar, and they dwelt there. Then they said to one another, "Come, let us make bricks and bake them thoroughly." They had brick for stone, and they had asphalt for mortar. And they said, "Come, let us build ourselves a city, and a tower whose top is in the heavens; let us make a name for ourselves, lest we be scattered abroad over the face of the whole earth." But the LORD came down to see the city and the tower which the sons of men had built. And the LORD said, "Indeed the people are one and they all have one language, and this is what they begin to do; now nothing that they propose to do will be withheld from them. Come, let Us go down there and confuse their language, that they may not understand one another's speech." So the LORD scattered them abroad from there over the face of all the earth, and they ceased building the city. Therefore its name is called Babel, because there the LORD confused the language of all the earth; and from there the LORD scattered them abroad over the face of all the earth. (Gen. 11:1-9)
Although Scripture is not overtly negative concerning Nimrod, his involvement establishing the first kingdom and initiating a building project which resulted in a severe judgment from God (the introduction of languages) clearly indicates his sinful ambitions.
Babylon has from its inception symbolized evil and rebellion against God. It was founded by Nimrod (Gen. 10:9), a proud, powerful, God-rejecting ruler. Babel (Babylon) was the site of the first organized system of idolatrous false religion (Gen. 11:1-4). The Tower of Babel, the expression of that false religion, was a ziggurat; an edifice designed to facilitate idolatrous worship. God judged the people's idolatry and rebellion by confusing their language and scattering them over the globe (Gen. 11:5-9). Thus the seeds of idolatry and false religion spread around the world from Babylon, to take root wherever these proud rebels and their descendants settled. 
There is also abundant tradition concerning the rebellion of Nimrod:
Now it was Nimrod who excited them to such an affront and contempt of God. He was the grandson of Ham, the son of Noah,—a bold man, and of great strength of hand. He persuaded them not to ascribe it to God as if it was through his means they were happy, but to believe that it was their own courage which procured that happiness. He also gradually changed the government into tyranny,—seeing no other way of turning men from the fear of God, but to bring them into a constant dependence upon his power. He also said he would be revenged on God, if he should have a mind to drown the world again; for that he would build a tower too high for the waters to be able to reach! and that he would avenge himself on God for destroying their forefathers! 
According to the Sages, Nimrod was the primary force behind this rebellion. The Midrashim explain his sinister motive. He planned to build a tower ascending to Heaven and, from it, wage war against God. 
The Targum of Jonathan says, "From the foundation of the world none was ever found like Nimrod, powerful in hunting, and in rebellions against the Lord." The Jerusalem Targum says, "He is powerful in hunting and in wickedness before the Lord, for he was a hunter of the sons of men, and he said to them, 'Depart from the judgment of the Lord, and adhere to the judgment of Nimrod!' Therefore as it is said, 'As Nimrod is the strong one, strong in hunting, and in wickedness before the Lord.'" The Chaldee paraphrase of I Chronicles 1:10 says, "Cush begat Nimrod, who began to prevail in wickedness, for he shed innocent blood, and rebelled against Jehovah." 
In the founding of Babel was the foundation for what would later flower as Babylon under Nebuchadnezzar and figure so highly in the events of Scripture, especially the book of Daniel which we have seen is key to understanding much of the book of Revelation.
Another negative connotation concerning Babel may be seen in the proverb taken up by Isaiah concerning the king of Babylon:
Take up this proverb against the king of Babylon ... How you are fallen from heaven, O Lucifer, son of the morning! How you are cut down to the ground, You who weakened the nations! For you have said in your heart: 'I will ascend into heaven, I will exalt my throne above the stars of God; I will also sit on the mount of the congregation on the farthest sides of the north; I will ascend above the heights of the clouds, I will be like the Most High.' Yet you shall be brought down to Sheol, to the lowest depths of the Pit. Those who see you will gaze at you, and consider you, saying: 'Is this the man who made the earth tremble, who shook kingdoms?' (Isa. 14:4, 12-16)
The connection between Satan (here Lucifer ) and Babylon is seen in this proverb which begins with the human king in view, but soon goes far beyond what could be said of the human king to identify the spiritual power motivating the king (cf. Eze. 28:12). Since Satan has been active in the affairs of the world since the creation of mankind, it is no surprise to find his influence in the realm of corrupt kings and kingdoms extending far back in history. Portions of the proverb, "Is this the man who made the earth tremble, who shook kingdoms", appear to speak of the ultimate king of Babylon at the time of the end, the Antichrist:
Isaiah thus makes the Babylonian monarch speak according to the ideas of his people ... and at the same time reflects the satanic spirit of self-deification to appear in fullest development in the last king of Babylon, the Antichrist (Rev. 13:8). 
Prior to the introduction of languages by God, the majority of mankind refused to disperse across the globe, but gathered in the region of Shinar instead. The result of the introduction of language was the scattering of different language groups over the face of all the earth (Gen. 11:9). This initial centralization, followed by the global distribution, is the primary mechanism by which Babylon became the central influence in all cultures and civilizations which followed. This is how she came to sit on "peoples, multitudes, nations, and tongues" (Rev. 17:15).
In the record of Babel, as minimal as it is, we see the first human king and kingdom in direct rebellion to the commands of God resulting in judgment. In Babylon of the end, we will see the last human king and kingdom in ultimate rebellion to the commands of God resulting in the final judgment of all human kingdoms to be replaced by the Millennial Kingdom ruled by Messiah.
 Translations differ as to whether Nimrod established Nineveh: "From that land Asshur went forth and built Nineveh...." [Tanakh: The Holy Scriptures: A New Translation of the Holy Scriptures According to the Traditional Hebrew Text (Philadelphia, PA: Jewish Publication Society, 1997, c1985) Gen. 10:11-12], [Scherman, ed., Tanach (New York, NY: Mesorah Publications, Ltd., 2001) Gen. 10:11]. If "the land of Nimrod" means "Assyria" in Micah 5:5-6, then that would lend support for the view that Nimrod established Nineveh.
 John MacArthur, Revelation 12-22 : The MacArthur New Testament Commentary (Chicago, IL: Moody Press, 2000), Rev. 14:8.
 Flavius Josephus, The Complete Works of Josephus (Grand Rapids, MI: Kregel Publications, 1981), s.v. "Antiquities I, iv 1."
 Scherman, Tanach, Gen. 11:1-9n.
 Donald Grey Barnhouse, Revelation (Grand Rapids, MI: Zondervan Publishing House, 1971), 294.
 Merrill F. Unger, Unger's Commentary on the Old Testament (Chattanooga, TN: AMG Publishers, 2002), Isa. 14:13.