http://www.answers.com/topic/eye-of-providence
"In its current form, the symbol first appeared in the west during the 17th & 18th centuries, but representations of an all-seeing eye can be traced back to Egyptian mythology and the Eye of Horus. 17th-century depictions of the Eye of Providence sometimes show it surrounded by clouds. The later addition of an enclosing triangle is usually seen as a more explicit trinitarian reference to the God of Christianity."
"On the seal, the Eye is surrounded by the words Annuit Coeptis, meaning "It [the Eye of Providence] is favorable to our undertakings". The Eye is positioned above an unfinished pyramid with thirteen steps, representing the original thirteen states and the future growth of the country. The combined implication is that the Eye, or God, favors the prosperity of the United States."
"The first official Masonic reference to the Eye of Providence is in The Freemasons Monitor by Thomas Smith Webb in 1797, some years after the Great Seal was designed. The Masonic use of the Eye does not incorporate a pyramid, although the enclosing triangle is often interpreted as one.
It is a popular urban legend or conspiracy theory that the Eye of Providence and unfinished pyramid show the influence of Freemasonry in the founding of the United States. This was recently dramatised in the Disney film National Treasure.
Although Benjamin Franklin, one of the members of the original design committee for the Great Seal, was a Freemason, it appears that he was not responsible for introducing the symbol, and may not even have been aware of it. Many masonic organisations have denied any special connection."
http://www.msana.com/stb_eyepyramid.htm
"A pyramid, whether incomplete or finished, however, has never been a Masonic symbol. It has no generally accepted symbolic meaning, except perhaps permanence or mystery. The combining of the eye of providence overlooking an unfinished pyramid is a uniquely American, not Masonic, icon, and must be interpreted as its designers intended. It has no Masonic context."
"The eye in the pyramid (emblazoned on the dollar bill, no less) is often cited as "evidence" that sinister conspiracies abound which will impose a "New World Order" on an unsuspecting populace. Depending on whom you hear it from, the Masons are planning the takeover themselves, or are working in concert with European bankers, or are leading (or perhaps being led by) the Illuminati (whoever they are). The notion of a world-wide Masonic conspiracy would be laughable, if it weren't being repeated with such earnest gullibility by conspiracists like Pat Robertson."
http://www.state.gov/documents/organization/27807.pdf
"Reverse Side of the Great Seal
The pyramid signifies strength and duration:
The eye over it and the motto, Annuit Coeptis (He [God] has favored our undertakings), allude to the many interventions of Providence in favor of the American cause. The date underneath is that of the Declaration of Independence, and the words under it, Novus Ordo Seclorum (A new order of the ages), signify the beginning of the new American era in 1776."