I personally like any of my parties to have a theme. Once I had did the idea of the CrAzY Professor and his lab and patients. I used old pickle jars, tomato jars, anything clear w/ a lid, and I stuffed them w/ indgredients from the fridge and water. The "specimens" were totally disgusting! (Especially since it was one way I would clean out my fridge...) If you label each jar and on a piece of paper you write down what each jar contains, you can turn it into a guessing game where the person w/ the most right wins a prize.
Ex:) I had old pizza, so I put it in the jar w/ water and labeled it "Patient #1-Brains" and on the paper I write down the Patient # and what I really put in the jar.
It's fun and different, and you can buy cute little prizes at any local dollar store, like Halloween glow sticks or a Halloween make-up kit.