Love was in the air—and gracing celebrity wrists—at Cartier as brand ambassadors such as Eva Mendes, Djimon Hounsou, and Rihanna came out to represent their favorite causes at the jewelry company's 2007 Love Charity Bracelet event on Thursday night. "This initiative is so tremendous and generous," said Julianne Moore, whose plum-colored bracelet will benefit the Tuberous Sclerosis Alliance. "Tonight is a nice way to celebrate the charities and bring some awareness to them." The bracelets—which retail for $475, with $100 going to charity—were available for sale, but many of the evening's A-list guests had their eyes on Cartier's bigger baubles. "I'm not much of a jewelry person on my own time," admitted 2006 ambassador Rosario Dawson, who accessorized with a pavé diamond bangle. "But when I dress up, it all comes out. It's a bit of a Cinderella effect." And Rachel Weisz? "My wedding ring is vintage Cartier," she said. "So I wear it all the time."

—Katie Hintz