Stars at Fashion Rocks

Dynamic duo Justin Timberlake and Beyonce lit up the stage of Radio City Music Hall when they channeled Marvin Gaye and Tammi Terrell for a performance of "Ain't Nothing Like the Real Thing" at the fifth annual Fashion Rocks concert in New York. The two also kept it down in Motown for earlier solo performances: Justin was as smooth and sexy as always, singing Gaye's "Got to Give It Up," and Beyonce tore down the house belting out "At Last" by Etta James (who was in the audience!) giving the crowd a preview of what's to come when she plays the iconic singer in the upcoming film Cadillac Records.

-Nakisha Williams

Rihanna

channeled her inner Material Girl in a whimsical costume during an electrifying performance of Madonna's "Vogue." The songstress stepped out of the feather detailing to reveal a beaded mini dress and dripped in Chopard jewels-including their million dollar diamond drop earrings and a diamond cocktail ring.

Even after a busy day of hitting Fashion Week shows like Julie Haus and Jason Wu, Leighton Meester arrived all smiles looking gorgeous in a Grecian Missoni dress. "I really want to see Beyonce tonight," the Gossip Girl said, "and Mariah Carey! I saw her at the Teen Choice Awards and she's fabulous!"

Taylor Momsen

turned heads and shocked audiences when she arrived in a punk-inspired look by BCBG Max Azria. "I live in my dark makeup…I wanted to do something different!" the Gossip Girl said of her look when she arrived with designer Azria. Later in the show, Momsen chatted with fellow presenter Miley Cyrus (in Zuhair Murad) backstage.

When actor Terrance Howard introduced Chris Brown, he noted that the young star will be wowing audiences for years to come. Brown proved Howard's point with an electrifying performance: he began with a silky cover of Sam Cook's "Cupid" before pumping up the volume with an acrobatic performance-complete with trampolines!- of his latest single, "Forever." Though Brown took to the stage in a dapper blazer and slacks, he told us, "My favorite fashion staple is sneakers."

Rihanna

(in Monique Lhuillier) arrived on the red carpet solo, but took a moment to pose with fellow R&B singer Mary J. Blige (in Roberto Cavalli). Later in the show, Blige hit the stage with Kid Rock to do an updated version of the Temptations' hit "(I Know) I'm Losing You."

Mariah Carey

took it back to the '70s when she performed her new disco-themed song "That Chick," in a glitzy Pamella Roland crystal and sequin tulle evening gown. Earlier in the evening, the songbird joined Beyonce, Mary J. Blige, Rihanna, Fergie, Miley Cyrus, Ashanti, Natasha Bedingfield, Keyshia Cole, Ciara, and Leona Lewis on stage for an ensemble performance of "Just Stand Up," a song created for the "Stand Up to Cancer" initiative, which the night's event benefited.

"I'm only going to one show this year-Rag and Bone," Charlize Theron told us on Thursday at Barneys New York. Friday, Theron arrived at Radio City having seen the show and wearing a rocker-chic look by the design house. The actress posed with singer Ashanti, who arrived in a Bollywood-style Marchesa dress.

Chace Crawford

and Hayden Panettiere were among stars who mingled backstage during performances. The Gossip Girl star dressed up a T-shirt and jeans with a Versace blazer, while the Heroes actress shimmered in a sequined Ferragamo mini.

Hilary Swank

was striking in a satin one-shoulder wrap dress with matching strappy sandals and an Amrapali cuff. The actress was among the celebrities-including Molly Sims, Vivica Fox and Tyra Banks-who came to enjoy the show.

Fergie

took the stage with Debbie Harry to perform the Blondie star's 1980 hit, "Call Me." The Dutchess also reunited with The Black Eyed Peas to pay tribute to the Rolling Stones with a funkadelic rap version of their hit "Miss You."

"Tonight I watched Serena [Williams] in the U.S. Open semifinals while other people got me ready!" admitted actress Elizabeth Banks (in Stella McCartney, Lorraine Schwartz jewels and Sergio Rossi shoes). This event kicked off her Fashion-Week itinerary which includes front-row seats at Peter Som, Phillip Lim and Monique Lhuillier. "I'm really excited about the younger, newer designers," said Banks. "Monique Lhuillier has accomplished so much and I think she's younger than me, though I don't want to repeat that out loud!"