Corpse Bride, The
Creature From the Black Lagoon, The
Crow, The
Dr. Jekyll & Mr. Hyde (1932, 1941)
Dracula (1931, 1977, 1992)
Frankenstein (1931, 1994)
Frankenstein, Bride of (& other sequels)
Halloween I & II
Halloween is Grinch Night
Ichabod & Mr. Toad
Invisible Man, The (1933)
It's The Great Pumpkin, Charlie Brown
King Kong (1933), Son of Kong
Mummy, The (1932)
Nightmare Before Christmas, The
Nosferatu (1922)
Old Dark House, The
Phantom of the Opera (1925, 1943)
Sleepy Hollow (1999)
The Simpsons: Treehouse of Horror (1-7, 12, increasing every time a new season is released)
Werewolf of London, The
Wolf Man, The
Young Frankenstein
I'm surprised that a few of those more modern flicks haven't gotten a mention before now.
I also have some "See Also" films that are very Halloween-friendly that aren't in my October-only collection:
Batman, Batman Forever (Returns is in my Christmas "See Also" cross-reference)
Beetlejuice
E.T.
Ed Wood
Edward Scissorhands
Ghostbusters
Hannibal Lecter movies
Harry Potter movies
King Kong (2005)
Practical Magic
Psycho
The Day The Earth Stood Still
The Goonies
The Mummy (1999)
The Shining
Willy Wonka
Wizard of Oz
Not surprisingly, there's a lot of Tim Burton stuff on the list.