Many people who are too old to trick or treat (or go on a pub crawl) like to rent or purchase horror movies to watch. Granted many popular websites and magazines have "Scariest of All-Time" list, but most of those are films made during the last four decades. Some lazy people give you films made only since 2000. I'm going to give you different choices.
Traditional: The Universal monsters are always good for Halloween. That includes these set featuring Frankenstein, Dracula and the Wolfman. Add to that the Hollywood's Legends of Horror Collection, which included Bela Lugosi and a proto-Goth Chick in Mark of the Vampire, Boris Karloff as politically incorrect villain Fu Manchu, the early color film Doctor X and it's boring sequel staring Humphrey Bogart, Mad Love with Peter Lorre as a Stewie Griffin prototype and Devil Doll with Lionel Barrymore as a Mrs. Doubtfire prototype. Also try out Frederic March's version of Dr. Jekyll and Mr. Hyde.
A Ton of Fun for a Good Price: Check out Mill Creek's Horror Classics 50 Movie Pack. Some great stuff and a few clinkers, but for under $20 bucks in most stores.
For kids: Try to find Mad Monster Party featuring the voices of Boris Karloff, Phyllis Diller and Gale Garnett. There is also the 70's Saturday morning cartoon the Groovie Ghoulies.
Ultimate pick: It's a DVD (pic above) put out a few year ago by Something Weird called Monsters Crash the Pajama Party (Spook Show Spectacular). The title movie is a hokey beach party thing with guys in gorilla suits running around, however if you can maneuver the tricky menu on this you will find several things including Bert I. Gordon's Tormented (a psychological ghost thriller), an anti-cable TV ad using art work from Famous Monsters magazine, monsters movies made by kids from the 20's and 30's (seriously these are good), monstrous musical numbers from the Big Band era (one features a dancing skeleton puppet) and a goofy 50s educational film called Don't Be Afraid of the Dark (the sequel was called Don't Wet the Bed).
Bad Cinema at It's Finest: Andy Milligan's 1970 Vampire film the Body Beneath. Filmed in Highgate Cemetery (fooled some Brits who thought vampires were in Highgate) with red-headed-green vampire women in prom dresses, a hippie hunchback is set on fire and nailed to a church door, a maid has her eyes poked out with knitting needles and the fat ghost of Queen Victoria spouts anti-American sentiments. Here is the trailer to get you interested.
HAVE A HAPPY AND SAFE HALLOWEEN!