Marc Summers' Mystery Magical Special - Summers, then known as the host of Double Dare, hosted this special that also featured magician Lance Burton. Summers is driving a small group of kids home and gets a flat tire. Seeking a phone in a nearby mansion, they witness several odd occurrences (my favorite was always a lady dancing with a mop wearing a jacket and hat) and watch Burton sword fight a masked villain. I loved this special, but not many people seem to remember it. One of the kids was Shiri Appleby, who later was one of the stars of the show Roswell and the movie Swimfan. Another kid was Jonathon Brandis, who later supported Rodney Dangerfield in Ladybugs.
Disney's Halloween Treat - Another special from the 80's that my parens had on a VHS tape. I used to watch this every year. It's basically a clip show featuring spooky or scary moments from other Disney presentations, as well as footage of the Haunted Mansion ride. There were parts that I was always a bit creeped out by, but my sister was flat out terrified by.
The Pumpkin Who Couldn't Smile - A special that starred Raggedy Ann and Raggedy Andy. They help a jack-o-lantern that, as the title implies, can't smile. He's sad because no one wants him, so he cries pumpkin seeds, which is pretty adorable. They also manage to cheer up a kid who's aunt is grumpy.
Garfield's Halloween Adventure - Garfield and Odie encounter ghost pirates in an attempt to get candy. Probably one of the more well-known of the specials on this post, since I know several people that loved the old Garfield specials. No link because I couldn't find a decent quality video.
It's The Great Pumpkin, Charlie Brown - Another classic. I'm pretty sure anyone reading this probably know it. No video again.
Are You Afraid Of The Dark - This show was a running series for a few seasons, so it's not really a special. But there were two early episodes that always stood out to me around Halloween"
- "The Tale Of The Twisted Claw" - After a prank at an old lady's house the night before Halloween, two boys are given a special treat by the lady when they go trick-or-treating at her house: a twisted claw capable of granting wishes. The wishes, however, come at a price. This was I think the pilot that aired before the series started as a special.
- "The Tale Of The Nightly Neighbors" - When an Eastern European family moves in the next door wearing all black and having a fondness for night, a brother and sister suspect that they may be vampires. Just another episode of the series, but it's one of the ones that stand out in my memory.
I feel like I'm forgetting at least one or two. I may have to update this later. Feel free to add your own in the comments section.