Nick Cannon promised an "insane night." And it was.

Six acts were vying for America's Got Talent Season 7's top prize - $1 million and a Vegas show.

But before a winner could be crowned Thursday, NBC packed the two-hour finale with clips of bad past talent, judges' quips from throughout the season, a surprise visit from Joan Rivers, a farewell from Sharon Osbourne and lots of star performances, including Justin Bieber, live from Newark.

Judges Howard Stern, Howie Mandel and Osbourne, who were all dressed up for the occasion, had the best job of the night. All they had to do was sit in their judges' seats, front and center, and watch all the fun.

"Look, this was the first season for me," said Stern. "I never would have imagined when we started this journey together that here we would be with such incredible talent. When we first started I said, 'I don't know. Are we going to find anybody?' But we've found some incredible people. And it's been an honor to be here for this first season."

Interspersed with walks down memory lane from the judges, the finalists teamed with star acts for duets.

Flo Rida sang his single I Cry while David Garibaldi and his CMYK's knocked out a cool painting of the rapper/singer.

Ne-Yo danced and sang Let Me Love You.

William Close caressed his giant earth harp as accompaniment to One Republic performing Feel Again.

Olate Dogs and The Untouchables performed while Frankie J (just back from touring with Jennifer Lopez and Enrique Iglesias) sang.

Grandfather of rap Burton Crane performed his Watcha Gonna Do with Nick Cannon.

"It's been an amazing year," said Mandel. "Especially with our new judge, Howard Stern. It was a thrill. I wanted to do something special as a gift for him. I wanted to surprise him." He then played video of eliminated contestant Big Barry, 70, known as the little guy with the big heart, surprising Howard backstage. (It wasn't hilarious.)

Blue Man Group unveiled a new electronica act filled with lights and giant floating balls.

Comedian Tom Cotter then "roasted" the judges.

"Who are these guys to judge us?" he said, digging into the trio. "Seriously. You've got a germophobic game show host, the bride of the Prince of Darkness, and Fartman. Please."

He continued, "What do we know about them? We know that Howie lives in L.A., that Howard lives in New York City, Sharon lives in a castle in England. And Nick lives in Mariah Carey's house."

He was then interrupted by Joan Rivers. "You're too nice," she told Cotter, pushing him aside. "So let me show you how to do it."

Said Rivers, "Look at this panel. If I want to see three people who make tons of money and have no talent, I will not watch you guys. I will watch the Kardashians."

She told Stern they'd been friends a long time. "I go back with you (to) when you were funnier than Imus." That brought boos and groans from the audience.

She joked about Osbourne's beauty and Mandel's germophobia. Cotter then came back and tackled each of them again. He noted (with the very old joke) that Stern has a "face for radio because Howard looks the bastard child of Joey Ramone and Big Bird." And Mandel. "What do you go in a barbershop and say can I have the look of a gay pirate?" (This prompted Mandel to sport an eye-patch after the show.) And Osbourne? "She speaks two languages fluently - English and Ozzie."

Next up: Joe Castillo created a piece of sand art, showing a globe that became a child's face, as members of the P.S. 22 elementary school chorus performed Edge of Glory.

Finally, eliminations began. First act to go home: The Untouchables kid dance troupe. "Don't be sad, little one," said Osbourne, as the camera cut to weeping dancer Ruby, "because it's my last show too. So we're both leaving together. Hand-in-hand."

Second act to go home: Joe Castillo. He smiled and graciously thanked the show and fans.

"The shame of tonight is that there can only be one winner," said Mandel.

Third act to go home: David Garibaldi and his CMYK's.

Next up: Justin Bieber, surrounded by dancers, sang As Long As You Love Me to shrieks from the crowd and help from rapper Big Sean. They were followed by Green Day, who performed Oh Love.

Third place finisher: Gasp! William Close, the giant earth harpist. The crowd was stunned and unhappy. But Close was cool. He said, "I made it to third place on this amazing stage, and that rocks."

So it came down to comedian Tom Cotter and the Olate Dogs.

Richard Olate, 55, held one of his dogs tightly, burying his head in the pooch's fur at times. So cute! His son, Nick Olate, held and petted a smaller dog as they waited for the announcement.

At last the winner was named: Gasp again! It's Olate Dogs!

Confetti rained down, covering the dogs and everyone else. Hugs were shared all around as all the acts came back on stage.

Tom Cotter went out with a final joke, saying the experience was "great. And I'm going to fall down the stairs to get my own million dollars tonight."