I believe in ghosts, but not all ghosts are bad. Some ghosts are helpful and/or trying to teach you a lesson. Here are some examples:
-The Ghost of Presents Past from the "Arthur" segment "Prunella Gets It Twice".
-The Ghost of Christmas Present from "A Christmas Carol"
-Casper The Friendly Ghost
-Ghostwriter from the PBS TV series
-Sam Wheat from the 1990 film "Ghost"