Las Vegas goes crazy for Labor Day weekend, and none othe than Will.i.am kicked off the party Friday at Encore Beach Club at Encore Las Vegas.

Hundreds of fans were treated to a performance by the singer and his Black Eyed Peas bandmate apl.de.ap.

PHOTOS: Will.i.am Gets The Party Started At Encore Beach Club In Las Vegas

Nicole Scherzinger -- the Pussycat Dolls lead singer-turned-judge on Simon Cowell's new The X Factor -- was so moved that she joined the superstar musician in the DJ booth and showed off some of her sexiest dance moves.

The music and party kept going until sunset and that was just the first afternoon!

PHOTOS: Simon Cowell & Mezghan Hussainy Vacation On The Mediterranean

RELATED STORIES:

PHOTOS:  Simon Cowell's Bride-To-Be Flashes Her Engagement Ring

PHOTOS: Actors Who Can Sing

PHOTOS: American Idols! Our Favorite All-American Bikini Babes

Playboy founder Hugh Hefner hosted his annual Midsummer Night’s Dream party Saturday night and RadarOnline.com has all the pictures from the super sexy summer fling.

With new girlfriends Anna Sophia Berglun and Shera Berchard on his arm, Hef invited Hollwood heavyweights to the Playboy Mansion for a night of debauchery.  

PHOTOS: Hugh Hefner’s Sexy Summer Fling

Captain America star Chris Evans partied with bad boy Jamie Kennedy, while Glee’s Mark Salling and Max Adler were on hand to watch the hundreds of gorgeous women dressed in their “favorite sleepwear and lingerie” party until the early hours of the morning.

It was a busy weekend for Hollywood’s hottest stars, who were out and about across the world dressed in the best, worst & wackiest fashions. RadarOnline.com has all the photos in our weekend roundup.

PHOTOS: Stars In The Best, Worst & Wackiest Fashions Of The Weekend

Leighton Meester brought out the bombshell for the Los Angeles premiere of The Roommate. The Gossip Girl, who is always a wild card on the red carpet (we will never be able to forgive her for that awful Marchesa jumpsuit) looked totally fab in a Pre-Fall 2011 Michael Kors collection black chiffon jersey leather cut out gown, which she paired with Harry Winston earrings and Brian Atwood heels.