Flag Day itself commemorates the day in 1777 that the Continental Congress adopted the flag known as the "Stars and Stripes." Answers.com has a lot of good background information on the design and history of the flag — click here for the article.
Here is the wording of the resolution passed by that Congress:
Resolved, That the flag of the United States be made of thirteen stripes, alternate red and white; that the union be thirteen stars, white in a blue field, representing a new Constellation.The symbols of those stars and stripes are very important, and the ideals for which they stand have inspired people around the world to accomplish great things over the 230 years that the flag has evolved. The field of stripes represent the rebellious original 13 colonies and their stand for independence against imperialism. The "canton" of white stars on a blue background was to be the constellation by which others would navigate their way toward democracy and the principles of human freedom, equality and dignity that the political system was meant to safeguard.
Of course the flag has been used for more sinister, selfish and restrictive purposes over the years. Many have used it as a symbol of narrowing nationalism, meant to separate the established from the new comer. Others have used it as a symbol of a new kind of economic imperialism, the standard under which peoples in foreign lands would be exploited and manipulated.
With the current immigration debate hotly raging aross the country and beyond our borders, it's more important than ever for us to reclaim the original symbolism of our flag and use it as it was intended. Not as a way to play ourselves against others, or to promote the ridiculous notion that we are inherently better than competing nations, but to unite all those around the world who value equality, liberty and the pursuit of happiness.