Paris Hilton celebrated her 26th birthday in Las Vegas over the weekend with two dates for the big event. The Simple Life star celebrated at celebrity sushi restaurant Nobu with her sister Nicky Hilton, her boyfriend David Katzenberg and Nicole Richie and Joel Madden. According to veteran Hollywood gossip columnist Janet Charlton, Hilton had two dates for the evening, former boyfriend Stavros Niarchos and Brandon Davis. The socialite was seen hopping between Niarchos and Davis, alternately kissing one, and then the other, between bites of sushi. The cozy threesome also reportedly shared a room at The Palms Hotel and Casino.