While many of us don't like spiders on a regular day, they seem to become especially creepier around Halloween - and therefore make fantastically frightening decorations.
The spiders themselves can be crafted out of various materials. Paper is a good choice, or, to create a more realistic 3-D version, glue together Styrofoam balls that you've painted black. Add pipe cleaners for legs. Where to put your spider? In its web, of course.
Spider webs can be crafted out of string, especially good material if you want to make a web with intricate detail. If you'd rather have a wispy web, try stretching cotton balls or gauze, perfect for corners or a room or over bushes outside. You can also buy very inexpensive, pre-packaged "webbing" at most discount and drug stores.