Great Pumpkin as usual, it sets the mood perfectly. Night of the Living Dead used to come on TV every Halloween, so it's now a staple.
Throughout the month I load up on others: the rest of Romero's original zombie trilogy, most of the main Universal Monster movies (and at least one must-see sequel: The Bride of Frankenstein), classic slasher stuff, silent films, foreign horror, low-budget films both classy and trashy, etc. Tonight it'll probably be Carnival of Souls.