Phantasm, as a kid, scared the crap out of me and I still get creeped out when I think about it. I've seen bits and pieces since then, but won't watch the whole thing because I don't want to ruin the memories I have of it. Besides that, it doesn't look as if it's aged very well.
As a rule, I don't get scared by movies anymore. I'm a horror hound, though, so I'm probably just desensitized. BUT: the scene in The Thing where they're testing the blood, even though I've seen it 100 times, still makes me sweat.
Also, I didn't want to make a new thread for this, but every Halloween, every website around makes a list of the top 10/25/50/whatever horror movies. Most of these lists are pretty predictable and through the years they've gotten pretty stale. Here's a list that has some truly "wth?" picks, and their top 10 are mostly headscratchers (though I agree with number 1!). See if you agree:
http://www.boston.com/ae/movies/gallery/top_50_scary_movies