If you have a nostalgic turn of mind and grew up in 90s, then you might have a soft spot for really old websites. A nostalgic person might also cling to holidays with happy childhood memories.
I am such a person -- so here are some old 90s websites with Halloween themes.
Sorted by date
1996/11 - Unsolved Mysteries website. While there's nothing Halloween-ish on the website, I include it here because this show spooked the hell out of me as a kid. And that's what Halloween's all about, right? Also, it's one of the older pages I've found on The Wayback Machine.
1997/10 - Ghosts of North Portland. The site has a 90s look, but not aggressively so. It is included here because it's a good example of the kind of unique, interesting content that the first webizens worked really hard to put online. Plus it's a pretty spooky site (or so I thought when I first encountered it in about 1999).
1998/06 - Restin' Pete's Discount Bargain Burial Barn. A site mixing weak coffin jokes with old CG artwork (of coffins).
1998/10 - Halloween Eternal. A brief history of Halloween, updated for the 1998 Halloween season.
1998/12 - Billy Bear's Playground Happy Halloween page. Only Christian toddlers could enjoy this twee page on its own merits, but it's definitely valuable as an example of a fairly sophisticated page.
1998/12 - Bob's Halloween Page. Super-weird page. The centerpiece is a top-down CG map of a cemetery. Click parts of it to see 3D renders of that location.
1999/02 - Melissa's Free Halloween Gifs. Huge assortment of Halloween gifs.
1999/02 - Scary BeardBros Ani-Gifs. Halloween gifs. A little less cuddly than the usual fare (but still tame). Doom monsters rather than teddy bears.
2001/01 - Joan Stark's ASCII Art Gallery's season/holiday art. Three different galleries of Halloween or fall ASCII art. Pre-web ASCII art colored with lots and lots of HTML markup.
Undated; sorted by name
BJ's Halloween. Make sure to click all the "Enter" and "Follow" links! There's several pages of content here.
Bruce's Halloween Links. Long list of Halloween links, some of which still work (e.g, Tripod ones). Use the Wayback Machine for dead ones.
HALLOWEEN LINKS. Another long list of Halloween links.
Halloween Eternal. "Now updated for the 1998 Halloween season."
Horrorible Backgrounds. Halloween graphics, particularly backgrounds.
Krystal's Witches. A tribute mostly to Sabrina the Teenage Witch, with some Halloween gifs sprinkled in. As she says, "What is a witch without a pumpkin." Go up a directory for the scariest part of the site: "My name is Krystle. I was in a fire whenever I was 8 years old. Before the fire I used be bad! In the daytime I told my Mom I was going to park but really I was going to the swamp to catch frogs and tadpoles. I used to beat up my brother all the time! I used to stand up on my sled! My father and my brother died in the fire." Krystal's site also has ghost stories and a cybershrine to Limp Bizkit.
Mulder and Scully on IRC. How can you make the X-Files even more 90s? Write an X-Files fanfic on Geocities using green text and a black background. Still not 90s enough? Write your GeoCities X-Files fanfiction in the form of an IRC conversation. Halloweenish because X-Files.