Evolution of the United States Flag (from USFlag.org):
No one knows with absolute certainty who designed the first stars and stripes or who made it. Congressman Francis Hopkinson seems most likely to have designed it, and few historians believe that Betsy Ross, a Philadelphia seamstress, made the first one.

Until the Executive Order of June 24, 1912, neither the order of the stars nor the proportions of the flag was prescribed. Consequently, flags dating before this period sometimes show unusual arrangements of the stars and odd proportions, these features being left to the discretion of the flag maker. In general, however, straight rows of stars and proportions similar to those later adopted officially were used. The principal acts affecting the flag of the United States are the following:

On June 14, 1777, in order to establish an official flag for the new nation, the Continental Congress passed the first Flag Act: "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."

Act of January 13, 1794 - provided for 15 stripes and 15 stars after May 1795.
Act of April 4, 1818 - provided for 13 stripes and one star for each state, to be added to the flag on the 4th of July following the admission of each new state, signed by President Monroe.

Executive Order of President Taft dated June 24, 1912 - established proportions of the flag and provided for arrangement of the stars in six horizontal rows of eight each, a single point of each star to be upward.

Executive Order of President Eisenhower dated January 3, 1959 - provided for the arrangement of the stars in seven rows of seven stars each, staggered horizontally and vertically.

Executive Order of President Eisenhower dated August 21, 1959 - provided for the arrangement of the stars in nine rows of stars staggered horizon tally and eleven rows of stars staggered vertically.

Other Links / Information:
Flag Etiquette
Glossary of flag terms
The American Flag Foundation, Inc. (featuring information on the 2006 Pause for the Pledge)
America's Tallest Flagpole (with "live cam")
Worlds largest Flag
Flag Day at Military.com
Flag Day at Echo9er