With her pooch in tow, the Gossip Girl star celebrates her 21st b-day on the New York City set of her show. Plus: Ashlee Simpson, Lindsay Lohan, Paris Hilton and more

LOOKING SHARP

Christina Aguilera (in a Julien MacDonald dress) makes an elegant arrival Saturday at a party celebrating the Trump Tower Dubai at a private residence in Bel Air, Calif. The singer, who performed four songs at the bash, told reporters that being a mom to son Max, born Jan. 12, has helped her sense of style. Said Aguilera: "He only enhanced my figure in a way and he just makes me laugh and smile every day."