Here is a set of counting/number mats that would go great with any Halloween theme. Just add plastic spiders from the dollar store and you have a math activity ready to go. I backed my set with a contrasting color and laminated them for extra durability.
This activity works great with my class of preschoolers who have disabilities. They enjoy the simplicity of the background and have a lot of fun putting those spiders in the web. The added benefit of these mats is that they can be used for visual-perception as well. As an extension, playdough could be used instead of plastic spiders for children who have better developed imaginations.