NBC's Today show celebrated its 50th anniversary this morning with a three-hour clip-drenched extravaganza. Former hosts Jane Pauley, Joe Garagiola and, yes, even news rival Bryant Gumbel (now at CBS's Early Show) were among the Today show grads who returned to Studio 1A to help current hosts Katie Couric and Matt Lauer mark the occasion. Kodak moments: Gumbel and onetime partner Couric putting aside their differences to share a big hug for the cameras; frequent guests Kermit and Miss Piggy paying a special visit; and too-spirited-for-her-own-good newsreader Anne Curry miraculously staying calm amidst all the hoopla. The highlight of the special, however, was a moving retrospective by noted documentarian Ken Burns, who opened the segment by playing footage of the Sept. 11 attacks in reverse.