Katy Perry made the long flight from L.A. to London to cheer on husband Russell Brand at the London premiere of his new movie Arthur. Though the pop singer made a blink-and-you'll-miss-it appearance on the red carpet, she did make a lasting impression in an asymmetrical nude gown with a crystal embellishment by designer Philip Armstrong. Back in the United States, Serena Williams scored major style points at the launch of the Range Rover's latest model, and Ashley Tisdale spent time with her fans at a DVD-signing. See more photos from last night's hottest parties in the gallery!
MORE: All Party Photos!