Vince Vaughn Helps Wish Jennifer Aniston a Happy Birthday

When Jennifer Aniston and Vince Vaughn announced their split in December, their reps told PEOPLE they remained good friends – and it looks like they still are. Vaughn, 36, was a guest at Aniston's 38th birthday party on Saturday at the Beverly Hills home of her best friend, Courteney Cox. (Aniston's actual big day was Sunday.) The actor stayed for about two hours along with guests including Sandra Oh, David Spade, Patricia Arquette and Kathy Najimy. Vaughn previously showed his support for his ex at the People's Choice Awards on Jan. 10. They each earned trophies for their romantic comedy The Break-Up, and upon accepting his award, Vaughn thanked Aniston and called her "one of the great people in Hollywood." The two began dating in the summer of 2005 while filming The Break-Up. That June, Vaughn told PEOPLE of his costar: "She's awesome. She has just a wonderful warmth and likeability about her."