This actually started as just a list of cool movies that are online, but then I realized that they were all pretty ghoulish, as many of my favorites are. Also, while many movies show up on YouTube and get taken down, these are all fully legal and should be available for a long time. Enjoy!
5. Night of the Living Dead (1968).
"They Are Night Zombies!! They Are Neighbors!! They Have Come Back From The Dead!! Ahhhh!!" Bring it on, George Romero, bring it on.
4. Nosferatu (1922).
The F.W. Murnau classic. Moody, engrossing, and actually scary at a couple points. (And campy in many other parts.) If you find it hard to get into silent film, perhaps you should check this out after renting "The Shadow of the Vampire," which gives you all sorts of fun context and shot-for-shot recreations of the original.
3. The Man Who Knew Too Much (1934). In eight parts.
Directed by Alfred Hitchcock and starring Peter Lorre. That's right. Peter Lorre. The man who perfected being creepy, strange, and awesome before Christopher Walken was a spermatoza. Also, while Hitch claimed otherwise, most agree that it's superior to his 1950s remake with J-J-Jimmy Stewart.
2. Fritz Lang's "M" (1931).
Of course, now that I've confessed my deep love for Peter Lorre, you don't think I'd forget this one, do you? The only reason it isn't number one is that I think it's kind of sacrilege to watch such a textured black-and-white film on a YouTube screen (even though the quality's pretty good for YouTube). But if you've never seen it, just five minutes should convince you to run out and get the Criterion Collection DVD.
1. Mr Death: The Rise and Fall of Fred A. Leuchter, Jr (1999).
Talk about creepy, strange, and awesome. It's not technically suspense or horror; it's a documentary. But it's pretty chilling all the same. Definitely one of Errol Morris's best, perhaps second only to "The Thin Blue Line." And it's on Google Video, so it has higher resolution than the others on this list.