It's the anniversary of the 9/11 attacks, and events in New York, Washington, D.C., and Shanksville, Penn. are marking the somber occasion. In Washington, the Obamas held a moment of silence at the White House at 8:46 a.m., when the first plane hit the World Trade Center eight years ago. At a Pentagon ceremony, the president placed a wreath in honor of the 184 victims of the crash there. "Let us renew our resolve against those who perpetrated this barbaric act and who plot against us still," Obama said. "In defense of our nation, we will never waver." In New York, Vice President Biden placed flowers at the Ground Zero memorial site. And in Shanksville, Colin Powell and Interior Secretary Ken Salazar are on tap for a ceremony for the 33 passengers and seven crew members who died trying to wrest control of United Airlines Flight 93 from terrorists.