I attended a really nice Halloween party at the Roosevelt Hotel in Hollywood. It was also an event that helped spread awareness for breast cancer. There was a dating-like auction where people were bid on and the money went to charity. There were also really cool items from various movies given away via a raffle.
It was a big costume party with some photo-ops and karaoke. There were some well-known cosplayers in attendence, as well as other celebrity guests.