SIMI VALLEY, CALIF. - Former First Lady Nancy Reagan praised her late husband Sunday, laying a wreath on his grave and singing "Happy Birthday" with the Beach Boys, as actors, musicians, former advisers and friends paid tribute to Ronald Reagan on the 100th anniversary of his birth.

Nancy Reagan greeted the crowd of about 1,500 invited dignitaries under a tent on the east lawn of the Ronald Reagan Presidential Library in Simi Valley.

"I know that Ronnie would be thrilled," the 89-year-old Reagan said, looking skyward, "and is thrilled, to have all of you share in his 100th birthday. It doesn't seem possible, but that's what it is."

After a crowd including son Ron Reagan and former Vice President Dick Cheney rose to its feet in applause, she shouted, "Happy Birthday, Ronnie!"

Nancy Reagan has made frequent appearances at the library but rarely speaks.

Former Cabinet secretary and close Reagan friend James Baker III and actor Gary Sinise were among many spoke in praise of the Gipper.

"The Reagan Revolution did not end when he left office 22 years ago, or when he left Nancy and all of us on June the 5th, 2004," said Baker. "Yes, the revolution was about a man, but it was really much more. The lessons Ronald Reagan taught us about freedom, and common sense and self-reliance remain every bit as true today as they were then."

Lee Greenwood sang his signature version of "God Bless the USA," a Reagan favorite, and several other singers, including country artists Lonestar and Amy Grant, also performed.

A group of FA-18 fighter jets based on the carrier USS Ronald Reagan flew over the crowd.

Reagan, the nation's 40th chief executive, was 93 when he died after a long battle with Alzheimer's disease.

The event was the culmination of a week of tributes to the former president at and around his presidential library, including speeches from Cheney and Sarah Palin.

In Illinois, where Reagan spent the first two decades of his life, hundreds celebrated at a birthday party at the Tampico Historical Society, eating cake and touring the nearby restored apartment where he was born in 1911. He graduated in 1932 from Eureka College, which held a Super Bowl party Sunday to honor its famous alum.

A special church service was dedicated to him at First Christian Church in Dixon, where Reagan was baptized.