Dead Little Girl - "The Ring":
Wear a white nightgown. Get a long black or dark brown haired wig from a costume shop (or if your hair is long enough, use your own hair).
Use lots of gel to make hair appear wet, arrange hair in front of face. You can pour water on yourself to make your hair and nightgown wet, if you so desire.
Whenever someone talks to you, say "Seven days" in the creepiest voice you can. Scares the pants off of anyone!
Thanks to Lilangelchick for this scary idea!