Caught in the Act! Britney, Matthew, Brad & More

12/27/2006 at 06:00 AM EST

• Britney Spears, partying up a storm with pals at L.A. hot spot Les Deux. The pop diva, who was having a "great time," really rocked out when DJ Stonerokk played her request – her own hit "I'm a Slave 4 U." Says an onlooker: "She danced all night."

• Kate Hudson, picking up takeout from Blue Plate in Santa Monica. The actress was sporting big sunglasses – and a huge grin – as she walked out with her food.

• Lindsay Lohan, partying with two gal pals at L.A. hot spot Social Hollywood. The actress, who's in AA, drank water on the rocks and was "rocking out to (Paul McCartney's) 'Silly Love Songs,'" says an onlooker. "She was having lots of fun."

• Brad Pitt, scoping out the designs at West Hollywood tattoo parlor Mark Mahoney's Shamrock Social Club. No word if Pitt got inked, but "he looked hot," says an onlooker.

More Celeb Spotting

• More Celeb Spotting

• Ashlee Simpson, visiting big sis Jessica on the set of her film Blonde Ambition in Shreveport, La., where the younger Simpson was immediately put to work. "It looks like her job is to carry around Jessica's little dog (Maltipoo Daisy)," an insider tells us.

• Mischa Barton, helping younger sister Hania pick out clothes at the LF Larchmont store in Los Angeles. Barton's face "instantly lit up" when she saw a fellow shopper's puppy, an onlooker tells us.

• Julia Roberts and husband Danny Moder, taking in a concert at the Anaconda Bar at the upscale El Monte Sagrado hotel in Taos, N.M., where the couple spent the holidays. Wearing jeans, a crewneck sweater and with her hair pulled back, Roberts seemed relaxed and happy, says a fellow concertgoer. The couple sat at the bar with friends while country singer Michael Hearne performed holiday-themed tunes.

• Ivanka Trump, enjoying food and conversation with a small group of girlfriends at New York's Le Bilboquet, while a nearby table of girls from Trump's alma mater, the Chapin School, celebrated a birthday. When their cake came out to the tune of 50 Cent's "In da Club," Trump and her gal pals threw their hands in the air.

Matthew McConaughey

Stewart Cook / REX

• Clint Eastwood and a large party, including son Kyle Eastwood, dining at Brentwood's Katsuya. When a guest gave Eastwood a present – a box of Wet Ones baby wipes – the director started laughing. "There was lots of holiday cheer at their table," a fellow diner says.

• Matthew McConaughey and a female friend, dining at West Hollywood eatery Sushi Roku. The pair nibbled on rice, black cod and bluefin tuna sushi. "They were laughing and really enjoying themselves," a diner tells us.

• By VANESSA DIAZ, JOCELYN JEFFERY, MARK LAMBERT, KIMBERLY LANSING, MARY MARGARET and INEZ RUSSELL