http://www.pinterest.com/pin/49328558393750451/
These "cauldron coolers" from Pinterest look really good! They aren't alcoholic but you could add some of the berry infused vodka's that are out there.
My Hubster loves the Cruzan brand of Black Cherry Rum - you could easily make a shake with chocolate or vanilla ice cream with that.
The below link has a variety of Halloween-themed drinks. Most could probably turn into some kind of shake if you wanted.
http://magazine.foxnews.com/food-wellness/10-creepy-halloween-cocktails-spook-your-guests