In the past I've run Halloween themed adventures. I've done things with haunted buildings and try to really play up how their is something wrong at the location. Wolves in the forest, lots of mist/fog making it hard to see and trying to give the abandoned structure a "lived in" feeling. I've also used the death knight template (MM2 v3.5) to make a headless horseman monster/boss. The group enjoyed that.
My favorite thing to do for Halloween, though, is to replace minis with candy. Whatever you kill, you get to eat. And then for the big bad at the end of the dungeon I try to put something down that everyone wants and to make it big. At least a king-size bar.
If you're looking for ideas, have you played either Thief: The Dark Project or Thief Deadly Shadows? Return to the Haunted Cathedral and Robbing the Cradle are some good sources of inspiration. Seriously, I cannot understate how much I've used the Thief series for inspiration in the past.
I have run I6-Ravenloft multiple times for my group in whatever game system we were playing at the time. The replayability of that module is tremendous. Unfortunately, we are all busy with other things tomorrow so we won't be gaming on halloween this year. Maybe we'll pick it up next month.
My normal game runs on Saturdays, so we're definitely gaming that day.
I often run Halloween themed adventures for this season.
My most successful ones have revolved around taking classing monster or horror movies and turning them on their heads.
For example, consider the idea of a community where it's suspected there are Werewolves. People have been found, killed, their throats ripped out and their bodies torn by animals.
A local nobleman offers a reward for the head of the Werewolf (proof required), and organizes the villagers to go out on the nights of the full moon to try and catch the monster.
The nobleman, by the way, is a Vampire, and he's behind the whole thing. No Werewolves, just him and some of his vampiric abilities. Remember that, aside from turning to a bat or mist, a Vampire can become a wolf or dire wold as a standard action, and can use the "Children of the Night" ability to call for a pack of wolves once per day. These less commonly used abilities make a perfect cover for a story like this one.