One of the annual favorites around Halloween.
Pre-Club Photo Booth
Great night to get good photos. Delegate to a high schooler to shoot the pics and upload them to facebook.
Instead of the usual mixer, hold a costume contest. Build a run-way. Invite everyone wearing costumes to participate. Identify the best costumes before club starts, as those folks cross center stage, pull them aside. Once you have the top 5-10 and everyone else is sitting down, vote by audience applause. Give a good prize.
If your "Costume Club" happens to fall AFTER Halloween, you can get a good deal on pumpkins. Hold a pre-club "pumpkin smash."
Monster Mash, Thriller, etc...
What other suggestions would you add?