Thousands of people attended the dedication, The Washington Post reported. Former Poet Laureate Robert Pinsky read the names of the dead with a bell tolling twice for each one.
The plane, bound for San Francisco, became the fourth flight hijacked on Sept. 11, 2001, shortly after takeoff from Newark, N.J. Passengers who learned that three other planes had been flown into the World Trade Center and Pentagon from cellphone conversations tried to overpower the hijackers, leading to the crash in Shanksville, Pa.
"With their brave decision they launched the first counteroffensive in the war on terror," former President George W. Bush said. "Americans are alive today because the passengers and crew of Flight 93 chose to act, and we will forever be grateful."
Former President Bill Clinton, who also attended the ceremony, promised to organize a Washington fundraiser to help bring in the $10 million needed to finish the memorial.
Vice President Joe Biden also attended.
The centerpiece of the memorial is the crater made when the plane hit the ground at more than 500 miles per hour. A 17-ton sandstone boulder marks the impact site.
The names of the 40 people who died on the plane are on a wall engraved in white marble. Further plans include a Tower of Voices containing 40 wind chimes, built 93 feet high.
Pot vending machine to debut
Pistorius testifies he didn't consciously pull trigger when he shot girlfriend