phenomena
blair and jc have posted some awesome 70's and 80's cinematic theme music in the last couple days, so i thought i'd pitch in. here's the main theme from italian horror master Dario Argento's 1985 film "Phenomena" (which, aside from being a great horror flick, starred a 14 year old Jennifer Connelly).
The soundtrack to Phenomena along with most of Argento's movies was done by the italian prog-rock band Goblin. Until I discovered Goblin, I really had no idea how creepy and menacing that 80's synth sound could really be.
insound.com has a bunch of Goblin albums for sale which you should buy. You can't really do much better for halloween music. As a bonus, here's "Jennifer's Friends", also off the Phenomena soundtrack. If you like horror movies, you owe it to yourself to watch everything Argento ever worked on.