Marble Hornets (scary/creepy stuff within ;))
 

For ease of use here is the introduction video - http://www.youtube.com/watch?v=Wmhfn3mgWUI

From then on it goes in number order (Entry 1, Entry 2, and so on).

The basic gist is a guy's friend was making a movie called Marble Hornets, then suddenly stopped, his mate managed to get him to hand over the videos, and after a few years, he went to view them and post the interesting stuff from them.

It gets more and more weird as it continues.

I also advise people keep an eye out for the ToTheArk poster who gives some video responses from around entry 9.

I apologize for any sleepless nights, whether it's through fear, or just the need to find out more (I wound up being the second one).

Beware of Slender Man ;).