Just in time for Halloween! 
If you have twenty minutes of your life to spare and want to be scared shitless by Internet mythology and novice filming (we heart indie webisodes) watch The Slender Man entries by Marble Hornet. There are about 29 videos, spanning from 40 seconds to 5 minutes... serious awesomeness. We're frightened and you should be frightened too.

Start at the beginning.
Finish when you get to the end.

Marble Hornets Video Channel