Starting in Los Angeles on Saturday, actress Kate Hudson hosted her annual house party -- where she welcomed Nicole Richie and Joel Madden. Rocker Madden dressed as a gynecologist and Richie as Gwyneth Paltrow's character Margot Tenenbaum from "The Royal Tenenbaums."
Other attendees at the Hudson bash included Amanda Seyfried, Adam Sandler, Gwen Stefani, Rachel Zoe, and Leslie Mann and Judd Apatow.
At Hollywood Forever cemetery, Adam Levine and his band Maroon 5 hosted a bash with Kirsten Dunst (as a flower child), Seth MacFarlane, Rose McGowan and Mischa Barton. The crowd sipped Bacardi cocktails and took in getups from the likes of Sophia Bush and boyfriend Austin Nichols, who dressed as newlyweds Katy Perry and Russell Brand.
Nearly 300 miles away, Sin City was treated to bashes from Snooki and Mike "The Situation" Sorrentino from MTV's "Jersey Shore." Snooki, dressed in a custom-made pickle costume (a nod to her favorite snack), reigned at Jet nightclub on Saturday. The Situation had hosted at the same venue the evening before, forgoing a costume but sticking close to an army of sexy zombies rocking Snooki's signature bump.
At Tao Asian Bistro, Ryan Kwanten of "True Blood" hosted Veuve Cliquot's annual Yelloween, in a gangster-inspired costume, while Audrina Patridge did a sexy take on Victorian garb at the Bellagio ...