Google has created some pages for the upcoming Halloween. On Google Video, you can find 14 short videos, including a teaser for "Hood of Horror". Google Books features a big list of famous scary stories, like Bram Stoker's Dracula or Mary Shelley's Frankenstein.
There's also a page that shows a Halloween party from 2000 at Googleplex. Google made a special logo for Halloween every year, as you can see here.
Google Maps Mania points to a list of mashups, from which the most interesting is HalloweenMashup, a site that helps you find Halloween events in the US.