Ashlee Simpson and Pete Wentz were out counting down to 2009 together with Heidi Montag and Spencer Pratt.

New mum Ashlee - who has ditched her red locks and gone back to blonde - hosted the New Years Eve party at PURE nightclub in Las Vegas with her husband.

And just one month after giving birth, the singer looked fabulous as she showed off her slim post-baby body in a tight-fitted black dress.

After dancing all night Ashlee and Pete led the countdown and then shared a very public kiss at midnight.

Other partygoers included Heidi Montag, Spencer Pratt and Kim, Khloe and Kourtney Kardashian.

See them ring in the New Year below